Pregnant Heidi Montag Pratt Celebrates Son Gunner's 5th Birthday: 'Biggest Blessing'

heidi montag, spencer pratt
heidi montag, spencer pratt

heidi montag/instagram (2)

Heidi Montag Pratt is celebrating her firstborn just weeks before becoming a mom of two.

On Sunday, The Hills alum shared a sweet video compilation that included photos and videos of son Gunner Stone over the years. The pregnant mom penned a heartfelt caption on her Instagram post celebrating her little boy's fifth birthday.

"Happy 5th Birthday my angel @gunnerpratt ✨ you truly take my breath away," she wrote.

"I thank God on my knees for you every day. Being your mom has been the biggest blessing," she continued.

Montag Pratt praised her little boy for being "loving, sweet, funny, fun, thoughtful, strong, smart," before adding. "Thank you for marking me a mama. Best day of my life 💕"

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Earlier this summer, Montag Pratt enjoyed some time with her little boy before he becomes a big brother, taking a "special alone trip" to what appeared to be Montag Pratt's Colorado hometown.

"I wanted to have a special alone trip with [Gunner] before the baby comes," Heidi shared on Instagram at the time.

"It was such a soul-filling trip taking my angel to the place that will always feel like home," the soon-to-be mom of two continued. "Such a blessing to have so much family time. 🙏🏼"

RELATED: Pregnant Heidi Montag Pratt Shows Off Her Baby Bump in Nude Maternity Shoot — See the Photo!

Heidi Montag Takes Son Gunner, 4, on Solo 'Soul Filling' Trip Ahead of Baby Number Two.
Heidi Montag Takes Son Gunner, 4, on Solo 'Soul Filling' Trip Ahead of Baby Number Two.

Heidi Montag/Instagram

Heidi and husband Spencer, 39, confirmed to PEOPLE in June that they are expecting their second baby, a boy.

While she isn't due until December, Heidi believes that her little one will make an early arrival, much like Gunner did back in October 2017.

"Gunner was three weeks early, so I'm anticipating that to be the norm. I've asked my doctor, like, 'Is that a reoccurring situation?' Basically, she said, 'Yes,' " Heidi recently explained to PEOPLE. "So if your body naturally kicks out babies early, you'll tend to do that."