William mourns the death of his mentor: Royals are 'shocked and saddened' as UK's third richest man, the Duke of Westminster, dies of heart attack - leaving his £9bn fortune to his 25-year-old son 

Hugh Richard Louis Grosvenor, who was asked to be Prince George's godfather by Prince William in 2013, will inherit his father's entire £9billion estate

The 25-year-old son of the late Duke of Westminster is set to inherit his father's entire £9billion estate.

Hugh Richard Louis Grosvenor, who was asked to be Prince George's godfather by Prince William in 2013, will also receive the family seat in Cheshire, Eaton Hall.

The inheritance comes after his 64-year-old father Gerald tragically died at Royal Preston Hospital in Lancashire on Tuesday.

A Buckingham Palace spokeswoman said that her Majesty the Queen was aware of the news about the Duke and will send a 'private message of condolence'.

And Hugh, who is now the 7th Duke of Westminster, will inherit his father's wealth, which includes around 100 acres of Mayfair and 200 acres of Belgravia - two of the most expensive areas in the UK.

The land is so costly that, in 2002, the Grosvenor Group sold a 65sq ft parking space in Mayfair for £65,000.

Unusually for the children of hereditary peers, Hugh and his three sisters, Tamara, Edwina and Viola, were educated at a state primary school on The Wirral, near their home before attending a private day school, Mostyn House.

Hugh and his siblings were later pupils at co-educational Ellesmere College in Shropshire.

The school costs up to £10,296-a-term to attend, with alumnae including rugby player Bill Beaumont and Michael Chapman, the former Archdeacon of Northampton.

He went on to study countryside management at Newcastle University, and later was a student at the University of Oxford.

After graduating, Hugh worked in estate management for the Grosvenor Group before becoming an accounts manager at coffee recycling firm bio-bean, which collects waste coffee grounds and converts them into biofuels and biomass pellets. 

Speaking of his son in 1992, the Duke had told The Independent: 'My main object will be to teach him self- discipline and a sense of duty. He's been born with the longest silver spoon anyone can have, but he can't go through life sucking on it. He has to put back what he has been given.'  

Hugh is the 6th Duke of Westminster's only son and although the young man has led a quiet life, he did celebrate his 21st birthday in style.

It was reported that his landmark bash cost £5million and featured an A-list guest list including Prince Harry. 

The Prince, 31, was among 800 guests who enjoyed entertainment from world-famous comedian Michael McIntyre and British hip-hop duo Rizzle Kicks.

The extravagant celebration was held in a marquee in the garden of the family's 10,872-acre estate in Cheshire, and photographers and the media were barred from the occasion.

The Duchess of Westminster (second from left) with her children Lady Edwina (left), Hugh (third from right), Lady Tamara (second from right), and Lady Viola (right). Lady Edwina's husband, Dan Snow is pictured next to the Duchess

Hugh will receive the family seat in Cheshire, Eaton Hall (pictured), which sits on a 10,872-acre estate, and is where the new Duke and his sisters grew up

At the time Hugh, who was a student at Newcastle University, told The Chester Chronicle: 'The party was simply amazing – a birthday and a party I will never forget.

'It is the beginning of a new era in my life and I look forward to the challenges that lie ahead.'

The dress code for his birthday party was 'black tie and neon' and it was reported that the security was so tight that the doors of vehicles taking guests to the party had been sealed with tape to prevent gate-crashers.  

He gave a speech in which he joked about growing up with his three sisters and thanked his parents for their unconditional love.

Vanity Fair described him as 'baby-faced' and 'absurdly rich', while the Tatler List declared: 'Hughie's a Newcastle graduate with his own wine collection who goes wild for girls in neon.'

Hugh's eldest sister, Lady Tamara, 36, married one of Prince William's closest friends Edward van Cutsem, at Chester Cathedral in 2004.

City banker Edward is Prince Charles's godson, and the brother of George's fellow godparent William van Cutsem. The wedding was attended by the Queen and the Duke of Edinburgh, and both William and Harry acted as ushers during the ceremony.

However, Prince Charles did not attend, reportedly after learning that Camilla Parker-Bowles, now the Duchess of Cornwall, had been assigned a seat several rows back.

The eldest of the Grosvenor siblings, Lady Tamara, 36, pictured left with her husband Edward Van Cutsem, and Lady Edwina, 34, (right) who is a keen campaigner for prison reform

Hugh, 25, pictured at Prince George's christening in 2013, and the youngest of the four siblings, Lady Viola, 23

The couple have two sons, Jake, born in 2009, and Louis, who was born in 2012.

Hugh's second eldest sister, Lady Edwina, 34, married television presenter Dan Snow, the son on veteran broadcaster Peter Snow, in Bishop’s Lodge in Woolton, Liverpool, in 2010, a far more low-key affair than Tamara's.

The couple met in 2008 at the wedding of her cousin, Rosie Innes-Ker, and have a daughter, Zia, born in 2011, and a son, Wolf, who was born in 2014.

Lady Edwina, whose godmother was Princess Diana, is a passionate prison reform campaigner, and helped set up The Clink chain of restaurants, which are located within prisons and staffed by inmates with a view to help them prepare for life after their release with a view to gaining employment.

She studied sociology and criminology at Northumbria University and has said her interest in helping prisoners began at a young age, and has spoken about her father taking her to meet recovering addicts at a drug rehabilitation centre in her early teens.

Hugh also has a younger sister, Lady Viola, 23, who is an ambassador for the anti-bullying charity Kidscape, which described her as 'extremely passionate about taking a hands-on approach to supporting vulnerable young people'.

She has said she wants to train as an art therapist in the hope of setting up her own charity for children and young people.

Hugh is likely to have to take on responsibility for the Westminster Foundation, the charitable body which manages the philanthropic activities of the Grosvenor family. It was set up in the 1970s and since then has awarded over £40 million in grants.

His mother Natalia, the Duchess of Westminster, is Prince William's godmother and his father was extremely protective of his four children.

He reportedly refused to send them to boarding school and enrolled them at a state primary before taking them to a private day school near the family home in Cheshire.

Despite the fact Hugh will take the largest share of the family fortune, his sisters are also set to inherit considerable trust funds.

He had insisted he wasn't interested in his wealth, saying in a rare interview: 'Not interested in material things. Honestly. It would drive me bonkers if I thought too deeply about it'

As the 6th Duke of Westminster, Gerald Grosvenor was Britain's richest property magnate, owning swathes of Mayfair and Belgravia and estates in Oxford, Cheshire and Scotland.

The duke was a close friend of senior royals and Prince Charles asked him to mentor his son William, who in turn asked his son Hugh to be godfather to Prince George.

He was made a Commander of the Royal Victorian Order – a personal gift of the Queen – in 2012, in addition to being a Knight of the Garter and a Companion of the Order of the Bath. He was an executor of Princess Diana's will.

Brought up in a remote part of Northern Ireland in a simple, rural, unaffected and unspoilt way, it was not until he was in his teens that it began to dawn on him that he was heir to a huge fortune.

The duke remembered his childhood on Ely island in the middle of Loch Erne as idyllic, frugal and isolated. Enniskillen, the nearest town, was seven miles away.

He said: 'Popping down to the corner shop to buy sweets was a bit of a safari. It was a wonderful foundation for life. I am a country person by birth and inclination.'

He hated his schooldays at Harrow, leaving with just two O-levels, and failed the entrance exam to the Royal Military Academy at Sandhurst.

He thought he would end up as a beef farmer in Northern Ireland. Then his uncle died and his father inherited.

'We had never talked about it,' the duke said. 'The great thing was that my father allowed me to be a child without thinking that I was going to be a duke, or that I should be different from my next-door neighbour.' 

Some believe he never really got over the fact that he was different. A friend remembers going up by train to visit him in Chester, thinking she would be picked up by chauffeured limousine.

Instead, it was just Gerald in a battered Land Rover and baggy corduroys.

Yet this was the man who owned 133,000 acres in Scotland, Lancashire and Cheshire.

He also controlled the most priceless land in central London – 300 acres in Mayfair and Belgravia, on some of which the American embassy sits. 

He was said to be introspective and his riches stopped him having close friends. Acquaintances describe him as a 'rather lonely man'.

He was once photographed sitting alone on a bench in Trafalgar Square eating a sandwich.

The duke insisted money was not important, saying in a rare interview: 'Not interested in material things. Honestly. It would drive me bonkers if I thought too deeply about it.'

The four passions in his life were his family, his businesses, his charities and the Territorial Army of which he became commanding officer and was especially proud.

He joined in 1970 as a trooper and moved up the ranks to be appointed a two-star general in 2004.

Close to a nervous breakdown some years ago, he cited his relative lack of personal achievement, and was desperate about failing to live up to the family motto 'Virtue Not Ancestry'.

One day he woke up and found he simply could not get out of bed.

He later recalled: 'At that moment all my wealth counted for nothing.' It was why the Territorials meant so much. 'It is something that he himself earned. It had nothing to do with being a duke,' said a friend.

Yet four years ago, he abruptly quit after a failed attempt to overhaul the TA's image. He wanted to change its name to Army Reserve, but was opposed.

The duke was also passionate about helping those less fortunate than him, working for many years with young offenders and drug abusers as well as campaigning on countryside issues. 

Primogeniture was also applied to the British monarchy until 2013 when the law was amended. As a result, Princess Charlotte will retain her place in the line of succession if her parents have another son

Although Hugh Grosvenor is the third of his father's four children, he will inherit the Duke of Westminster's title and his entire £9billion estate.

This is because of primogeniture, the right of the firstborn male child to inherit the family estate, even if he has older sisters - as is the case with Hugh. 

The Normans introduced the common law to the UK in 1066, and it puts male children ahead of female children, irrespective of age.

Variations on primogeniture have since modified the right of the firstborn son to the entirety of a family's inheritance.

Ministers have also labelled the rules 'discriminatory', and called for further talks about changing the laws, while critics of primogeniture include Lady Kinvara Balfour, whose grandfather was the 17th Duke of Norfolk. 

She hit out at the 'archaic, mad and bonkers' law last year, after her mother, Lady Tessa, missed out on inheriting Arundel Castle in West Sussex. 

Instead the property, which dates back 1,000 years to the reign of King Henry I, passed to her younger brother Edward.

The tale of succession is supposed to have inspired Lord Fellowes of West Stafford, a close family friend, to write Lady Mary's story in Downton Abbey, which sees Lady Mary denied the keys to the house, which passes to long-lost cousin Matthew Crawley. 

Primogeniture was also applied to the British monarchy until 2013, when, under the Succession to the Crown Act 2013, the law was amended before the birth of the Duke and Duchess of Cambridge's first child to ensure the throne would pass to them, whether it was a boy or a girl. 

This only applies retrospectively to people born after October 28, 2011, so it did not affect the current immediate line of succession.

The move brought the UK in line with most European monarchies, who had already established an equal law of succession.

It also means Princess Charlotte, will not be usurped from fourth in line to the throne if her parents go on to have any more sons.

Now only Spain, Liechtenstein and Monaco are left with the old system.