Who Is the Mystery Costume Designer at the Heart of the Alleged Three-Year Affair Rocking Lily Allen and David Harbour’s Marriage?

This one is messy. David Harbour and Lily Allen quietly split in late 2024, and now the fallout has gone public in a way that feels equal parts personal and PR grenade. There are cheating allegations, detective-level Raya sleuthing, a long-rumored on-set relationship, and a very real conversation about what any of this should mean for an actor still booking big jobs.

What kicked this all off

According to a string of tabloid reports, including one from the Daily Mail, Harbour allegedly carried on a years-long relationship with a younger costume designer while he was still married to Allen. The outlet says the pair met on a movie, were not particularly subtle about it, and that Harbour even footed the bill to get her to him — including flying her more than 400 miles to Atlanta while he was shooting Stranger Things.

The designer was not named by the publication. An associate quoted by the paper framed it bluntly, but the point is simple: the alleged romance overlapped with the marriage.

Meanwhile, Allen — who originally met Harbour on the celebrity dating app Raya back in 2019 — suspected something was off and, per the reports, went looking for proof. She supposedly rejoined Raya herself, setting her profile to look for women, and found a new profile that appeared to be Harbour’s. Friends in London told the paper she had a hunch he’d been open to meeting other people for a while, and that she only got clarity near the end of summer 2024.

Context that matters: Harbour spent the past year based in Atlanta for Stranger Things and even bought a house there in 2024 to be closer to the set. He is also one of Marvel’s key players, with Black Widow under his belt and Thunderbolts on deck. Allen, for those keeping the family tree straight, is the daughter of actor Keith Allen and producer Alison Owen.

• 2019: Harbour and Allen match on Raya.
• 2020: They get married in Las Vegas.
• Late 2024: The couple separates; reports surface alleging Harbour used Raya again and maintained a three-year relationship with a younger costume designer he met on a film.
• 2024: Harbour buys a home in Atlanta while filming Stranger Things; has largely been living there.

Allen on how bad it got

After the split, Allen took time away and has been unusually candid about how dark things got. She talked about food issues intensifying and the pain of staying sober through a period when, in the past, she would have coped by using. In British Vogue, she said the despair was overwhelming without that old escape hatch.

"The feelings of despair that I was experiencing were so strong. The last time that I felt anything like that, drugs and alcohol were my way out, so it was excruciating to sit with those feelings and not use them."

For the first time, she checked herself into a residential facility — her choice, which she called progress.

"I have been into those places before against my will, and I feel like that is progress in itself. That is strength. I knew that the things I was feeling were too extreme to manage, and I was like, 'I need some time away.'"

When asked what made this time different, she was painfully direct.

"That I wanted to die."

In Perfect Magazine, Allen said the marriage did not help her self-worth and dredged up long-standing issues with rejection and abandonment. She also described the confusion of piecing things together on her own because, as she tells it, answers were not forthcoming.

"I was not sure what was real and what was in my head. So there is a certain amount of joining dots. When you are not given answers, your brain is full of lots of questions."

She has also been clear-eyed about what relationships can and cannot fix.

"Being in a relationship is not the answer to all of my problems — in fact, it is probably the opposite."

Allen says parts of this experience are woven into her new record. None of that is surprising, but it is a reminder the fallout here is not just tabloid fodder — it is directly feeding her work.

The reaction online (and the part fans are arguing about)

Once the cheating allegations hit the rounds, X lit up — and people are not remotely aligned. Some say men can blow up their marriages for years and still collect franchise paychecks, and they want casting directors to stop rewarding that behavior. Others fire back that cheating is not a fireable offense, personal and professional lives should be separate, and if moral purity became the hiring standard, Hollywood would be a ghost town.

There is also pushback centered on Allen: several posters claim she has previously spoken about cheating on her first husband, Sam Cooper, including with female escorts, and argue it is hypocritical to cancel Harbour but not her. That last point is coming from fans, not a new report, but it is part of the current discourse.

Where this lands

None of the uglier allegations have been tested in court, the costume designer has not been named, and most of the narrative is coming through unnamed associates and magazine interviews. Still, the picture is pretty clear: a marriage collapsed, a Marvel and Netflix star is under a cloud of personal controversy, and Allen is trying to survive it while staying sober and putting the pain into music.

As for whether studios should care about a star’s private life when it comes to hiring — that argument is not going anywhere. Tell me where you land on it.