'Ciao, first trimester!' Pregnant Hilaria Baldwin flaunts her growing baby bump in her bra and underwear... after revealing she's expecting a baby boy

She's expecting her fourth child, a baby boy, with husband Alec Baldwin.

And on Friday, pregnant Hilaria Baldwin showed off her growing baby bump in a mirror selfie she shared to her Instagram.

The 33-year-old, who wore just her bra and underwear, captioned the photo 'Ciao first trimester.'

Glowing: Pregnant Hilaria Baldwin showed off her growing baby in a mirror selfie she shared to her Instagram on Friday

Glowing: Pregnant Hilaria Baldwin showed off her growing baby in a mirror selfie she shared to her Instagram on Friday

The mother of three put her hand above her growing midsection in the flawless snap, with her long brunette locks loose and wavy around her.

Hilaria beamed in the snap, opting to go makeup free.

The star wrote a lengthy caption, kicking it off with: 'Ciao first trimester!!!!  #BaldwinBabyBump4.'

Hilaria explained that during each pregnancy, she likes posting selfies showing her changing body.

Happy family: She's expecting her fourth child, a baby boy, with husband Alec Baldwin; seen on November 2 in NYC at the A Paley Honors Luncheon

Happy family: She's expecting her fourth child, a baby boy, with husband Alec Baldwin; seen on November 2 in NYC at the A Paley Honors Luncheon

'I try to stay as healthy as possible while pregnant but embrace slowing down, eating a bit more, and celebrating my changing body,' she said.

Adding in the Instagram post caption: 'We all go through these changes while pregnant. It's amazing, and I love to normalize it, rather than promoting being ashamed of gaining weight.' 

Hilaria and Alec, 59, are parents to three children together: daughter Carmen Gabriela, four; and sons Rafael Thomas, two, and Leonardo Angel Charles, 13 months.

Alec has a 22-year-old daughter named Ireland with ex-wife Kim Basinger.

Hilaria and Alec revealed the gender of baby number four in a very sweet way - by cutting a homemade cake with the inside as either pink or blue - to indicate the gender.

When she cut into the delicious treat, the inside of the cake was baby blue, revealing that their fourth child is a boy.  

Taking bets: Hilaria and Alec revealed the gender of baby number four in a very sweet way - by cutting a homemade cake with the inside as either pink or blue - to indicate the gender

Taking bets: Hilaria and Alec revealed the gender of baby number four in a very sweet way - by cutting a homemade cake with the inside as either pink or blue - to indicate the gender

Surprise: When she cut into the treat, the inside of the cake was baby blue, revealing that their fourth child is a boy

Surprise: When she cut into the treat, the inside of the cake was baby blue, revealing that their fourth child is a boy

She showed the blue colored cake in a video and a series of posts on her Instagram page, which she shared five days ago.

After the reveal, the soon to be family six enjoyed some of the dessert to celebrate the good news.

On Tuesday, Alec and Hilaria stepped out for a date night at the New York Fall Gala in the Big Apple.

The brunette covered up her pregnant belly in a strapless gown while Alec cut a handsome figure in his tuxedo.

Blessed: She showed the blue colored cake in a video and a series of posts on her Instagram page, which she shared five days ago

Blessed: She showed the blue colored cake in a video and a series of posts on her Instagram page, which she shared five days ago

Happiness: After the reveal, the soon to be family six enjoyed some cake to celebrate the good news

Happiness: After the reveal, the soon to be family six enjoyed some cake to celebrate the good news

The lovebirds began dating in August 2011 and tied the knot in June 2012 in New York City.

They had a renewal ceremony over the summer in honor of their five year wedding anniversary, which took place in The Hamptons. 

She spoke to People magazine about 'accidentally' giving her sons Ninja Turtle names.

Hilaria said of her fourth child - and third son: 'I can promise you that Michelangelo and Donatello will not be coming out of me.'

Sweet: The Baldwins revealed the gender of their fourth child in a playful way last week

Sweet: The Baldwins revealed the gender of their fourth child in a playful way last week

She jokingly revealed that her Instagram followers seem to think Donatello is the name most are guessing for baby number four.

The brunette said she gets name inspiration from artists because she 'was an art history major and I really love art. I wanted to give them artist names.'

Adding that: 'My family's in Spain and I wanted to have a name that could be pronounced easily in both languages.' 

The Teenage Ninja Turtles include Leonardo, Donatello, Michelangelo and Raphael. 

Full attention: Hilaria and Alec, 59, are parents to three children together: daughter Carmen Gabriela, four; and sons Rafael Thomas, two, and Leonardo Angel Charles, 13 months

Full attention: Hilaria and Alec, 59, are parents to three children together: daughter Carmen Gabriela, four; and sons Rafael Thomas, two, and Leonardo Angel Charles, 13 months

Glamourous: Alec and Hilaria enjoyed a date night on Tuesday at the New York Fall Gala in the Big Apple

Glamourous: Alec and Hilaria enjoyed a date night on Tuesday at the New York Fall Gala in the Big Apple

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