Lily Allen met David Harbour on dating app Raya. It's reportedly the same way she found him cheating.

Lily Allen and David Harbour have separated after four years of marriage, multiple sources have confirmed to PEOPLE.

"Her marriage has been crumbling and they have split," a source told the US publication exclusively.

The 'Smile' singer, 39, and Stranger Things actor, 49, reportedly broke up before Christmas last year, ahead of a planned holiday to Kenya.

Allen allegedly found Harbour on Raya — the celebrity dating app — after suspecting him of cheating.

Watch: Lily Allen talks about her journey to becoming comfortable about her sexuality. Post continues after video. 

Sources said Allen registered for the app and set her preference to 'women' in an attempt to catch Harbour out by cross-referencing women on the app with women the actor followed on social media.

"Lily was looking for women who were on Raya and cross-referencing them with women David follows on Instagram to try to figure out who he was seeing," a source said.

Allen reportedly uncovered a page belonging to the actor who wrote that he was "visiting New York from Atlanta". The latter location is where his hit show Stranger Things is filmed.

He also apparently described himself as a "closet nerd that plays tough guys on your TV", and the profile picture was of a dark-haired cartoon character smoking a cigarette.

"Lily has never even looked at anyone since she met David. She is devastated," said the same source.

It should be noted that neither Harbour nor Allen have publicly confirmed or denied these rumours of infidelity.

In January, the singer admitted she's "been spiralling" and suffering from "crippling panic attacks".

However, she did assure fans that she had not relapsed and would not be checking into a drug rehab centre.

"I know there's been some horrible blind items on the internet about me being found by my husband in a crack den, surrounded by men. I don't know who is spreading these vicious rumours but it's not true," Allen said on her Miss Me podcast.

"I'm finding it really hard to be interested in anything. I'm really not in a good place," she said on the podcast. "I know I've been talking about it for months but I've been spiralling and spiralling and spiralling and it's got out of control.

"I came to the Miss Me Christmas lunch and had a panic attack and had to go home. I went to see something at the theatre the other night with my friends Carla and Claire and I had to leave at half-time," she continued.

"I can't concentrate on anything except the pain that I'm going through."

The musician and actor were first linked in 2019 when they attended the BAFTA Tea Party together. They confirmed their relationship later that year on Instagram.

In 2022, Harbour reflected on falling in love with Allen after meeting on a dating app.

"I was in London alone, doing Black Widow, on this app, going on dates and stuff. And yeah, I started texting with her," the actor told GQ Hype.

"She was in Italy at the time –— we got together, went on a date at the Wolseley [a restaurant in Mayfair], and it was, you know, she's f**king unbelievable," he continued.

He also remembers the "exact moment" he fell in love with Lily on their third date.

"I was just in this phase, where I was like, I'm just going to be brutally honest about everything, because why lie? And I told her something about my life, about my beliefs… It would take a really extraordinary person to be accepting of the things that I said. And I remember thinking: 'Wow, that's somebody I want to be around,'" he said.

Harbour and Allen tied the knot in 2020 in Las Vegas.

In true Vegas fashion, the wedding was officiated by an Elvis Presley impersonator, and was followed by In-N-Out burgers.

"In a wedding officiated by the king himself, the people's princess wed her devoted, low born, but kind credit card holder in a beautiful ceremony lit by the ashen skies courtesy of a burning state miles away in the midst of a global pandemic," Harbour wrote in an Instagram post at the time.

He also praised his wife when speaking to PEOPLE, saying, "I married a beautiful, incredible woman who I love.

"I have never met someone who is so deeply kind as her. I've never felt so taken care of and cared for by another human being. She really is just a deeply kind individual and I love that about her." .

While they were together, Harbour became a stepfather to Allen's children — Ethel and Marnie — whom she welcomed with her ex-husband Sam Cooper.

Feature Image: Getty