The Oscar-winning actor's body was found in his New York City apartment on Sunday. He is believed to have passed away after suffering a heroin overdose as a needle was still in his arm when he was discovered.

He was 46, and last year checked into rehab as he feared he was relapsing following a 23-year period of sobriety.

Although it is not known when he began using again, two weeks ago he apparently spoke of his struggles to a journalist at the Sundance Film Festival in Utah.

Magazine publisher John Arundel initially didn't recognise Philip at the event, so asked what his job was.

"He said, ‘I’m a heroin addict,'" John told New York Post.

Philip then removed his hat, prompting John to realise who he was.

"I just got out of rehab," the actor said as he walked away, according to John, who added: "Obviously, he wanted people to know he was in recovery mode."

An autopsy has been carried out on the star's body, although it is not known when the results will be made available.

There are conflicting reports about the amount of drugs found in his apartment, with claims there could have been 20 empty bags of heroin, 50 full bags and 20 syringes.

Philip began renting the property for around $10,000 after he moved out of the home he shared with his long-term partner Mimi O'Donnell. The pair had been together for 14 years and have three children together, with Mimi reportedly asking the actor to leave the family home due to his addiction issues.

"It was known that he was struggling to stay sober, and his wife had given him some tough love and told him he needed some time away from the kids and to get straight again," an insider told the publication.

A law-enforcement source added: "He was apparently in the throes of a major heroin addiction."

There have been repeated reports that Philip was seen looking dishevelled over the last few weeks. Last week he was spotted apparently drunk in a bar in Atlanta and was then pictured seemingly passed out while aboard a flight to New York.

Neighbours of the star have claimed he was "troubled", with one telling the New York Post his issues were widely known about.

"Everyone knew he had substance-abuse problems," she said. "He did not look well recently - like he was out of it."

Mimi has reportedly told police she last saw the actor at 2pm on Saturday and thought he was under the influence of drugs. She spoke to him two hours later and again suspected he had taken something.

He was due to see his children on Sunday and when he didn't turn up Mimi contacted his friend David Bar Katz and British assistant Isabella Wing-Davey, who then discovered his body.

Mimi is now being comforted by actress Cate Blanchett, who worked with Philip on 1999's The Talented Mr. Ripley and has been photographed visiting the costume designer and her children.

Tonight Broadway will dim its lights in tribute to the late actor.