Ringing in a new decade with his loved ones. John Mulaney celebrated his 40th birthday with Olivia Munn and their son, Malcolm, 9 months.

“There is truly no better way to turn 40,” the comedian captioned a snap — which showed him with his baby boy on stage surrounded by balloons and streamers — via Instagram on Saturday, August 27.

“🙌 Last night was a blast. Happy birthday, John!” the official account for the Ryman Auditorium in Nashville, Tennessee, commented. Mulaney’s “From Scratch” comedy tour stopped at the iconic Music City venue on Thursday, August 25, and Friday, August 26, which was his birthday.

To celebrate hitting the milestone, Munn, 42, arranged an unexpected treat for the former Saturday Night Live writer. “Malcolm surprised John on stage last night to sing HBD with the whole audience,” Munn revealed via her Instagram story on Saturday.

She carried the infant onto the stage as the crowd sang to Mulaney. The comic was also given a tiered cake to celebrate, much to his son’s delight.

“And then [Malcolm] swiped some cake over John’s shoulder,” the X-Men: Apocalypse star revealed in another snap.

The new mom hadn’t planned on her son getting his first taste of cake while teething. “The look of a sugar rush. I guess we won’t be waiting til his one year birthday to give him his first taste of cake,” Munn captioned a happy selfie from the celebration.

The pair welcomed their baby boy in November 2021, nearly a year after Mulaney finished rehab amid a relapse in his sobriety.

“Olivia’s truly been his rock post-rehab and is super supportive of him,” a source exclusively told Us Weekly in June. “Being a father has certainly changed his perspective on life in that he realizes he has another human to take care of so he wants to be the best dad he can be and just be healthy and present for him.”

That doesn’t mean marriage is in the cards for the happy couple — at least not right now. “Olivia and John have only been together for a little over a year so they’re really not in a rush to get married. It’s definitely not her focus right now. She really wants to enjoy this time as a new mom,” the insider continued. “Olivia’s fully embracing motherhood and all its challenges and ups and downs.”

While they are not rushing down the aisle, Munn and Mulaney seem to be happier than ever. “Having a baby surely brought them closer as a couple,” the source noted.

Scroll down for photos from Mulaney’s 40th birthday celebration: