Mark Zuckerberg is celebrating wife Dr. Priscilla Chan on her birthday as they prepare to welcome a new addition to the family.
The Meta CEO, 38, shared a sweet birthday tribute in honor of Chan turning 38 on Friday, posting a cute picture of him giving his wife a kiss on the cheek while holding her baby bump. In the comments of the Instagram post, Zuckerberg revealed that the heartfelt photo was taken "in a science lab."
"Happy birthday to my favorite person! (Or, as August likes to call her, the main character in our family.)," he captioned the post.
Zuckerberg and Chan, who are expecting their third baby girl together, are already parents to two young daughters: August, 5, and Maxima "Max," 7.
Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.
Zuckerberg and his philanthropist wife first announced their exciting baby news in September.
"Lots of love. Happy to share that Max and August are getting a new baby sister next year!" he wrote alongside a sweet photo of the couple on social media.
In the photo, Zuckerberg placed his hand on Chan's stomach as the pair smiled for the camera.
Zuckerberg and Chan's love story began in 2003 when they started dating after meeting in line for the bathroom at a party at Zuckerberg's Harvard University fraternity when he was a sophomore and she was a freshman.
The couple moved in together in September 2010, he wrote on Facebook at the time. Then, in May 2012, they tied the knot in a ceremony in their Palo Alto backyard — surprising their guests, who thought they were there to celebrate Chan's graduation from UCSF medical school.
The pair recently celebrated their 10th wedding anniversary, commemorating the special milestone by recreating one of the photos they took together on their special day back in 2012.
"10 years married and half our lives together," Zuckerberg wrote alongside the recreated snap. "Here's to more adventures."