The Oscar-winning star, 46, was reportedly found by a friend who called emergency services, but Philip was pronounced dead at the scene. It is thought that the late actor, who checked into rehab last May, died of a heroin overdose.
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Gwyneth Paltrow was among the host of celebrities who expressed their shock and grief at Philip's sudden passing. The Hollywood actress, who starred with Philip in the 1999 drama The Talented Mr. Ripley, posted an old snapshot of herself and the late actor on set.
"Ischia 1998, post dinner, post shooting... Philip was a true genius. #philipseymourhoffman," wrote Gwyneth alongside the photo, in which co-star Jude Law and a female friend are also pictured.
Behind the scenes with Gwyneth and Philip on The Talented Mr. Ripley
Philip's last major role was in The Hunger Games: Catching Fire, in which he played Head Gamemaker Plutarch Heavensbee. Philip had reportedly finished filming the next instalment in the series, Mockingjay Part 1, and had seven days of filming left on the third film, Mockingjay Part 2. Producers have yet to reveal how they will cover his absence.
Hollywood beauty and Hunger Games protagonist Jennifer Lawrence described Philip as "such an incredible actor" and added that "he played an excellent Plutarch."
"PSH - I am genuinely shocked, saddened and speechless," wrote co-star Sam Claflin. "A truly wonderful man, with a magical touch. My hero. Thoughts are with his family."
Philip as Plutarch Heavensbee in The Hunger Games: Catching Fire
A joint statement from Jennifer, The Hunger Games' author Suzanne Collins, the films' director Francis Lawrence and producers Nina Jacobson and Jon Kilik also expressed their condolences.
"Words cannot convey the devastating loss we are all feeling right now," it said. "Philip was a wonderful person and an exceptional talent, and our hearts are breaking. Our deepest thoughts and condolences go out to his family."
Philip's co-stars and those he had worked with on previous films also revealed their shock and regret.
"I feel so fortunate to have known and worked with the extraordinary Philip Seymour Hoffman, and am deeply saddened by his passing," said Julianne Moore, who appeared with the late actor in Boogie Nights, Magnolia, and The Big Lebowski. "My thoughts and condolences are with his family."
Philip starring in Magnolia
"This is a horrible day for those who worked with Philip," said Philip's Charlie Wilson's War co-star Tom Hanks. "He was a giant talent. Our hearts are open for his family."
George Clooney, who appeared alongside Philip in The Ides of March, said, "There are no words. It's just terrible."
Other celebrities took to Twitter to express their sentiments, including Mia Farrow, who posted, "OH NO!!!!! Philip Seymour Hoffman has died. A truly kind, wonderful man and one of our greatest actors – ever."
"A tragedy to lose as supremely talented an actor as Philip Seymour Hoffman," tweeted Kevin Spacey. "An unspeakable loss for film, theatre & all who knew him. RIP."
"Phillip Seymour Hoffman was a genius, brave and sweet," wrote Susan Sarandon. "Can't believe he's gone. Huge loss. My deepest sympathy for his wife and children."
Philip, who won an Oscar for best actor for his performance in 2005's Capote, is survived by his three children whom he had with costume designer Mimi O'Donnell.