Can you see the smile? #babyboy #profile

A photo posted by Holly Madison (@hollymadison) on

Picture-perfect: Holly Madison’s unborn son can already mug for the camera like his model mom. The pregnant best-selling author proudly showed off a sonogram in which her little boy appears to be grinning in an Instagram post on Thursday, July 28.

“Can you see the smile?” the Girls Next Door alum captioned the shot, using the hashtags “#babyboy” and “#profile.”

Due in August, the star, 36, and her husband of almost three years, Insomniac Events founder Pasquale Rotella, confirmed exclusively to Us Weekly in March that they are expecting a baby boy. (They are already parents of 3-year-old daughter Rainbow.) “I’ve been really lucky and am not having a lot of nausea or anything,” she told Us at the time. “People always say this, but when it’s your second pregnancy, you almost forget you’re pregnant. You just know what to expect, and I’m not reading up on it every day like I was with Rainbow.”

She hasn’t had much downtime to study anyway. “I'm just busy chasing after my daughter, so the time is going by superfast,” she added. “I blinked, and half the pregnancy was over.”

Indeed, Madison’s little girl rarely leaves her side. “She’s doing that toddler thing right now where she wants to jump in our bed in the middle of the night,” she explained. “I'm like, "How are we going to stop this before the baby comes? We're not going to have room!"

So the Astoria, Oregon, native called in the reinforcements: her mom, Patsy Cullen. “I was like, ‘Mom, how do you get a toddler to stop sleeping in your bed?’" Madison recalled to Us. But she jokes that Mom wasn’t much help: “She said, ‘Um, I was never very good at that…’ I'm like, ‘Oh, great, thanks for the advice!’”

Although the author of The Vegas Diaries says her firstborn “really wanted a sister,” she thinks Rainbow will be a big help with her little brother. “She's really nurturing with her baby dolls, and she loves taking care of animals,” added Madison. “And I've been reading her a lot of big sister books!”

Can't get enough of Us? Sign up now for the Us Weekly newsletter packed with the latest celeb news, hot pics and more!