The actress is pregnant with the couple's first child, with John confirming the news during a visit to Late Night With Seth Meyers on Tuesday, Sept. 7.
"In the spring, I went to Los Angeles, and met and started to date a wonderful woman named Olivia—Olivia Munn," John told host Seth Meyers. "I'm going to be a dad. We're both really, really happy."
John began the interview by giving a rundown of his "challenging" past 12 months, which included entering rehab in September 2020 amid a battle with addiction struggles. The star explained that in October, he left rehab and moved out of the home he shared with now-ex-wife Anna Marie Tendler but that shortly after hosting the Halloween episode of Saturday Night Live, he relapsed with cocaine and alcohol.
"Then I continued using drugs—you and some other friends staged an intervention, as you recall," John told Seth, explaining this led to a two-month rehab stint that ended in February 2021. At this point in the conversation, the John Mulaney & the Sack Lunch Bunch star pointed out he initially met Olivia for the first time at Seth's September 2013 wedding to wife Alexi Ashe.
"It is a very lucky thing to have met this woman," John said of Olivia, calling the relationship "really beautiful." He added, "She's kind of held my hand through that hell, and we are having a baby together."
It's been a whirlwind road to parenthood for Olivia and her stand-up comedian beau, who were first rumored to be dating in May following John's split from his wife.
A source told E! News at the time that Olivia and John's romance blossomed from a years-long friendship, but noted that things between the twosome were still "new and not at all rushed." After all, the SNL alum had just completed the two-month rehab stint and was dedicated to maintaining his health.
"The focus for John is his recovery and Olivia fully supports that," the insider explained, noting, "She will continue to help him in whatever ways she can and be there for him."
In late June, the couple enjoyed their first public outing together in Los Angeles.
A month later on July 23, John, 39, officially put an end to his six-year marriage by filing for divorce from the artist. Anna Marie said in a statement following their split that she was "heartbroken" by the comic's decision to go to their separate ways, but wished him continued success in his recovery.
As for John and Olivia's rapid love story, the 41-year-old X-Men: Apocalypse star implied in a July interview that very few know the truth about their journey together.
"I think what's more surprising is how much is incorrect," she shared with New Beauty. "There is so much attention on things that aren't the truth. And if you speak up and try to say the truth, you're accused of being messy or just not believed. I've gotten used to it, but it hasn't made it easier."