‘Millie Bobby Brown filed a harassment and bullying claim before they started shooting the last season. There were pages and pages of accusations.’ We reveal the latest bombshell claims facing Lily Allen’s estranged husband David Harbour

They have always had a tumultuous on-screen relationship in Netflix’s hit series Stranger Things.

But now the Mail on Sunday can reveal actor David Harbor is facing shocking allegations that he ‘bullied and harassed’ co-star Millie Bobby Brown.

Mr. Harbour, 50, who is also facing allegations that he cheated on his estranged wife, singer-songwriter Lily Allen, plays former police chief Jim Hopper, who adopts Millie Bobby Brown’s character Eleven, in the series, which is about to air its fifth and final season.

The British actress is said to be facing an internal investigation after she allegedly complained about his behavior towards her.

While the outcome of the investigation is unknown, the Mail on Sunday understands the allegations do not include allegations of sexual impropriety. A source said: ‘Mille Bobby Brown made allegations of harassment and bullying before filming started last season. There were pages and pages of accusations. “The investigation took months.”

Netflix last night declined to comment on any investigations, but it is understood Ms Allen, who is gutted on new album Mr Harbour and claims he has cheated on her multiple times, has steadfastly supported her husband throughout the ‘brutal’ ordeal.

A source said: ‘Lily supported him throughout the whole process. It was a brutal time.’

Millie had a personal representative on set during the filming of the final series, which begins airing in the UK and US this month and is expected to be one of Netflix’s most watched series ever.

The broadcaster is so convinced the final season will be a huge hit that it’s releasing the finale in two parts, with the second ‘drop’ airing on Netflix at Christmas, with the final episode set to release in cinemas and on the streaming service on December 31.

“This will be a theatrical event,” a Netflix source said last night. ‘Nothing will overshadow this, not even the leading actor’s private life.’

The source added that it was ‘unfortunate’ that Mr Harbour’s personal troubles were making headlines at a time when Stranger Things fans were eagerly awaiting a global celebration to mark the end of the groundbreaking show.

Millie has gone from an unknown teenager to a global superstar worth a reported $50 million (£38 million) thanks to the series, which began airing in 2016.

The series helped transform Netflix from a video rental service to one of Hollywood’s biggest studios.

The source said: ‘Netflix will never comment on an internal investigation, but the fact that they haven’t denied it says a lot. Stranger Things helped put Netflix on the map. Millions of fans around the world are eagerly awaiting the finale. ‘Nobody wants anything to distract from that.’

Ms. Allen, 40, who is in Los Angeles this weekend, is celebrating the best reviews of her career for her new album, West End Girl, a painful account of the betrayals of her four-year marriage that led to its collapse last December.

Lily Allen is celebrating the best reviews of her career for her new album, West End Girl, which painfully chronicles the betrayals of her four-year marriage to David Harbour, which led to its collapse last December.

Last weekend, the Mail on Sunday revealed New Orleans costume designer Natalie Tippett’s Madeline, a song written about a woman with whom Bay Harbor had an affair and featuring actual text message exchanges between his wife and his mistress.

While Ms. Allen did not deny our story, she backtracked this week, saying ‘Madeline’ was a ‘composite’ of several women Bay Harbor allegedly dated.

A source said: ‘Lily has suffered a lot in her private life. There were a lot of tears, a lot of anger. He created some of his best art from this pain.

‘He’s in a great place now and isn’t out for revenge. ‘He’s really happy and pleased with how his fans have reacted to the album.’

There are suggestions that Mrs Allen’s attacks on her husband in the new album may have been a ‘publicity stunt’ to attract more attention, especially after Bay Harbor was seen taking her two young daughters to a Florida theme park last weekend.

But another source said: ‘Lily’s pain was real. He wants David to maintain a good relationship with the girls because they love him. He is their stepfather and he loves them.

Millie currently runs an animal rescue center in the US state of Georgia with her husband, American model and actor Jake Bongiovi, who they were photographed with earlier this year.

‘Lily was the product of a broken home, so she doesn’t want them to go through the same abandonment that she did.’

Ms. Allen has spoken frequently about her tumultuous childhood on Miss Me?, the award-winning podcast she hosts with her best friend, Miquita Oliver.

Her father, actor Keith Allen, left her mother, film producer Alison Owen, when she was just four years old.

The source added: ‘He doesn’t want history to repeat itself.’

Ms Allen and her brownstone in Bay Harbor, New York, have listed their brownstone home on the market for $8 million (£6 million).

Public records show the property is owned by a trust named after his two daughters.

Last night, representatives for Millie, who now runs an animal rescue center in the US state of Georgia with her husband, American model and actor Jake Bongiovi, refused to respond to multiple requests for comment.

Requests were also made to representatives of Bay Harbor and The Duffer Brothers, multimillionaire twins Matt and Ross Duffer, who created Stranger Things based on the 1980s sci-fi series they grew up on, but they did not respond.