Lily Allen was said to have been left in ‘agony’ when she allegedly found that her husband, Stranger Things star David Harbour, was using the celebrity dating app Raya.

But apparently what the British pop star did not know was that Harbour had also been having an affair for at least three years with a colleague.

The Daily Mail has been told that the American actor, 49, was romantically involved with a younger costume designer, whom the Mail has chosen not to name.

‘David cheated on Lily,’ an associate told this newspaper. ‘They met on a movie they did together.’ The source, who witnessed their interactions on set, said: ‘They weren’t very secretive about their relationship.’

So serious did the romance become that Harbour paid for the woman to travel more than 400 miles to visit him while he was working on his hit Netflix TV series last year.

‘David flew her to Atlanta while he shot Stranger Things to keep him company,’ the associate said.

The news broke yesterday as Miss Allen, 39, daughter of hell-raising actor Keith and film producer Alison Owen, was spotted picking up a rental car in London.

Holding a £2,000 Balenciaga bag, the singer and actress examined the Mercedes before setting off. Miss Allen, who has two daughters with first husband Sam Cooper, wed Harbour in Las Vegas in 2020 a year after they met on Raya.

The couple moved from London to New York, where she enrolled her children in school.

Harbour bought a house in Atlanta, Georgia, last year to be closer to the Stranger Things set.

The couple separated late last year after the singer, whose songs include the hit Smile, speculated that Harbour was using Raya.

The Mail on Sunday reported that she turned detective by joining the app herself, pretending to be ‘looking for women’, and allegedly found that he had set up a new dating profile.

Raya has more than 10,000 members and accepts only eight per cent of applicants. There are 100,000 on its waiting list.

Miss Allen’s London friends said she had suspected that her husband was interested in other women. A source previously revealed: ‘Lily is of the belief that he has been open to meeting new people for some time now, though she only found out at the end of the summer. He has been living in Atlanta for a year for filming.’ In January, Miss Allen took a break from Miss Me?, the podcast she presents with her friend Miquita Oliver, after she admitted she was ‘really not in a good place’.

She recently returned to the podcast, on which she criticised Harbour and mocked his abilities in the bedroom.

Harbour’s former lover declined to comment, while his spokesman said: ‘We don’t comment on private matters.’