While John, 39, and Olivia, 41, were busy celebrating the birth of their first child on Nov. 24, fans (and probably Anna Marie) were whipping out their calculators.
If Munn gave birth to a full-term baby, she likely got pregnant in February, the same month Mulaney got out of rehab.
News that John and Anna Marie were no longer together did not come to light until May, after it was reported that he was dating Olivia. Up until that point, fans were under the assumption that the Saturday Night Live alum was still with his wife of nearly seven years. He officially filed for divorce in July.
On top of the fact that Mulaney did not announce Munn's pregnancy until September, the couple has also not posted about their baby's birth. It was reported by numerous news outlets on Dec. 18.
The following day, Anna Marie – a 36-year-old artist and author – took to her Instagram account to post a photo of her in a colorful dress, sitting in front of a mirror in a hotel room at the Madonna Inn in San Luis Obispo, California.
It's the same hotel she visited back in July on what would have been her seventh wedding anniversary with John.
She captioned the snap, "Norman F******g Rockwell," which is the title song from Lana Del Rey's 2019 album.
Del Rey has previously said that the track is "kind of about this guy who is such a genius artist but he thinks he's the s--t and he knows it and he, like, won't shut up talking about it."
The song's lyrics include, "Goddamn, manchild. You f--ked me so good that I almost said, 'I love you.'"
"You're fun and you're wild / But you don't know the half of the s--t that you put me through / Your poetry's bad and you blame the news / But I can't change that and I can't change your mood," the lyrics continue.
"You're just a man / It's just what you do / Your head in your hands / As you color me blue," sings Lana at another point in the song.
Both Mulaney and Munn have seemingly gone to great lengths to paint the picture that their romance began after his marriage to Tendler ended.
It was during a September appearance on Seth Meyers' late-night talk show that John first spoke about his relationship with Olivia as well as her pregnancy.
"I went to rehab in September [of 2020], I got out in October, I moved out of my home from my ex-wife," he told the host.
In December of last year, he said he "went to rehab again, this time for two months. I got out in February, I lived in sober living for another month and a half. ... Then in the spring, I went to Los Angeles and met and started to date a beautiful woman named Olivia."
"I got into this relationship that's been really beautiful with someone incredible," he added. "And we're having a baby together. I was nervous when I was about to say the news!"
In between his rehab stints, Mulaney got a job working as a writer for Meyers' show. He thanked the host for his involvement with intervening on him, also noting to the audience that he first met Munn at Seth's 2013 wedding to Alexi Ashe.
Following the interview, a celebrity agent who claimed to have worked with Munn in the past told Page Six they were suspicious of both the series of events and the way in which Mulaney presented them.
"I don't think it's any coincidence that John broke the news of Olivia's pregnancy the way he did in terms of basically giving a timeline of his past few months – when he moved out of his house, how it was the spring when he fell in love with Olivia," the agent said. "It seems to me that he is going to great lengths to dispute the idea that he cheated."
Prior to John, Olivia dated other high-profile men, including Aaron Rodgers, Chris Pine, Matthew Morrison and SNL alum Will Forte.
"She has a demonstrated history of hanging out with and spending time with 'SNL' guys, so no way did their paths not cross, and there is the video of them together back in 2017," said the agent.
Indeed, Mulaney and Munn were seen on camera together for Jon Stewart's special, Night of Too Many Stars, during which Olivia was heard saying, "Hi, John!" as Mulaney walked past her.
At one point, she even publicly considered herself an "obsessed" fan.
Interestingly, sources close with Tendler told Page Six that Mulaney had actually asked her for a divorce after his second rehab stint in February and not after he left treatment in the fall of 2020, like he had said on Meyers' show.
In May, a Mulaney source told People that his relationship with Munn was "very new" and that the two "met at church in Los Angeles."
One insider told Page Six that claim "was BS, and Twitter immediately called Olivia out on it, saying she's known John for years."
"It isn't entirely clear when their relationship started," added the insider. "There have been rumors for months about her being pregnant, and it all just seems like a very tight timeline."
The Tendler source went on to say that "Anna Marie knew he was doing things with other women before he went to rehab in December. And his claims to friends that he was trying to protect her before he went away to rehab were rubbish, she didn't need protecting."
"John was using Anna Marie to protect himself. But still, she was very heartbroken that he decided to end her marriage, she was heartbroken how it went down, it wasn't something that she wanted, she wanted to work it out," added the source. "I am sure this news about the pregnancy will be very difficult for her."