In Netflix’s acclaimed series Stranger Things, the dynamic between David Harbour’s character, Jim Hopper, and Millie Bobby Brown’s Eleven has always been a rollercoaster. However, recent revelations suggest that the tension may have extended beyond the screen.

According to sources, David Harbour has been accused of ‘bullying and harassing’ his co-star Millie Bobby Brown. The 50-year-old actor, who portrays the gruff but lovable ex-police chief Hopper, is also embroiled in personal controversies, including allegations of infidelity during his marriage to singer-songwriter Lily Allen.

The Mail on Sunday reports that Harbour became the subject of an internal investigation following claims made by Brown, a British actress, regarding his conduct. Although the specifics of the inquiry’s findings remain undisclosed, it is understood that the allegations did not involve any sexual misconduct.

A source familiar with the situation explained, “Millie Bobby Brown filed a harassment and bullying claim before filming began for the final season. The accusations were extensive and prompted a lengthy investigation that spanned several months.”

While the outcome of the investigation is not known, the Mail on Sunday understands the allegations did not include claims of sexual impropriety. A source said: ‘Millie Bobby Brown filed a harassment and bullying claim before they started shooting the last season. There were pages and pages of accusations. The investigation went on for months.’

Last night, Netflix declined to comment about any investigation, but it is understood that Ms Allen, whose new album eviscerates Mr Harbour, claiming he cheated on her multiple times, steadfastly supported her husband throughout the ‘brutal’ ordeal.

A source said: ‘Lily supported him throughout it all. It was a brutal time.’

Millie had a personal representative with her on set while filming the final series, which will start airing in the UK and US later this month, and is destined to be one of Netflix’s most-watched shows ever.

David Harbour with his Stranger Things co-star Millie Bobby Brown

The streamer is so convinced the final season will be a massive hit that it is releasing the finale in two parts with the second ‘drop’ on Netflix over Christmas and the final episode is being released in cinemas on December 31 as well as on the streaming service.

‘It will be a theatrical event,’ a Netflix source said last night. ‘Nothing is going to overshadow this, not even the leading man’s private life.’

The source added it was ‘unfortunate’ that Mr Harbour’s personal woes have hit the headlines at a time when Stranger Things fans were looking forward to a global celebration to mark the end of the groundbreaking show.

Millie went from an unknown teen into a global superstar worth a reported $50million (£38million) thanks to the series, which started airing in 2016.

The series helped transform Netflix from a video rental service into one of the biggest studios in Hollywood.

The source said: ‘Netflix will never comment on an internal investigation, but the fact they’ve not denied it speaks volumes. Stranger Things helped put Netflix on the map. Millions of fans around the world have been anticipating the finale. No one wants anything to take attention away 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, which painfully charts the betrayals in her four-year marriage which led to its implosion last December.

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

Last weekend, the Mail on Sunday revealed that New Orleans costume designer Natalie Tippett is Madeline, a song written about a woman Mr Harbour had an affair with and which includes real text message exchanges between his wife and his mistress.

Ms Allen, while not denying our story, appeared to backtrack this week saying ‘Madeline’ is a ‘composite’ of several women Mr Harbour allegedly had flings with.

A source said: ‘Lily went through a lot of pain in private. There were a lot of tears, a lot of angst. She created some of her best art out of that pain. 

‘She’s in a great place now and not seeking revenge. She’s really happy and delighted with her fans’ response to the album.’

There have been suggestions that Ms Allen’s attacks on her husband on the new album may be a ‘publicity stunt’ to drum up more attention, particularly after Mr Harbour was spotted taking Ms Allen’s two young daughters to a Florida theme park last weekend.

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

Millie now runs an animal rescue centre in Georgia, in the US, with her husband, American model and actor Jake Bongiovi, pictured together earlier this year

‘Lily was the product of a broken home so doesn’t want them to have the abandonment issues she had.’

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

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

The source added: ‘She doesn’t want history repeating itself.’

Ms Allen and Mr Harbour have put their New York brownstone house on the market for $8million (£6million).

Publicly available records show the property is in a trust named after her two daughters.

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

Requests were also made to Mr Harbour’s representatives and to The Duffer Brothers, the multi-millionaire twins Matt and Ross Duffer who created Stranger Things based on the 1980s sci-fi series they grew up on, but they have not responded.