This is the first child for both Zak, 36, and Olivia.
Zak's father Robin Williams died of suicide at the age of 63, almost five years ago.
The Hook actor was a dad to son Zak (his mother is Valerie Velardi), daughter Zelda, 29, and son Cody, 27.
Zelda Williams took the first official photo of her nephew.
"News is finally out: I’m an auntie! 🍼 Meet Mclaurin Clement Williams, aka Mickey, aka Dr. Baby! He’s a squishably cute pterodactyl cooing tiny wonder and I love him so much already ♥️ big shoutout to Mickey on being the fastest swimmer, and huge congrats to @heyoliviajune and my big bro @zakpym on creating this little joy (and poop) factory! 👶🏻 by Zak and Olivia"
Meanwhile, new mum Olivia spoke out about her newborn.
"Introducing you to my little family! My fiancé, Zak, and I were so happy to welcome baby McLaurin to the world on May 22nd. We are beyond thrilled he chose us to be his parents, and obviously think he’s the best, smartest, and cutest baby ever!! In life today, we expect everything to be live shared on social media, and many who are close to me are even just learning this news. 😬"
" We’ve kept this news private for a number of reasons, one of which is my increasing emphasis and appreciation for living life away from social media and focusing on my offline relationships, another being the challenges that face us as women startup founders. I have a lot more to say about this later, but at a high level... "
"Becoming a mom is something I’ve always known I wanted, but as an early stage startup founder sometimes sounded impossible, not because I didn’t think I could manage it, but because I knew the extent of bias in the industry against me as a female founder and the fight to be taken seriously in building a business focused on solving social challenges for women."
" (Not to mention the fact that maternity leave doesn’t exist for me!) As I’m proud to have successfully built a business that doesn’t rely on Silicon Valley VCs caring about women’s friendships to operate and has an amazing supportive team, I’m excited to be expanding my role from global change-maker startup CEO, connecting millions of women to their best friends, to a milk factory, raising a really amazing little man who has a boss mamma. None of this would be possible without the most incredible and supportive partner a woman could ever hope for."
"Zak, the headline is true, you’re already and will always be, “World’s Greatest Dad!” Mickey and I are the luckiest. 🥰 [Photos by my super talented future sister-in-law @zeldawilliams]"