George Clooney claims his late pal Matthew Perry "wasn't happy" during his stint on 'Friends' despite landing his dream job.

The 62-year-old former 'ER' star knew the late actor - who is best known for playing Chandler Bing on the legendary sitcom - from when he was a teenager and they were often reunited when filming their respective NBC shows on the same soundstage.

The '17 Again' actor was tragically found dead in his hot tub in October, aged 54, with an autopsy revealing he died from the "acute effects of Ketamine".

Matthew had been open about his battle with substance abuse and George has admitted that "success and money" wasn't going to save the deeply unhappy star.

He told Deadline: "I knew Matt when he was 16 years old.

"We used to play paddle tennis together. He’s about 10 years younger than me. And he was a great, funny, funny, funny kid."

George - who had a cameo on 'Friends' - continued: "All he would say to us, I mean me, Richard Kind and Grant Heslov, was, I just want to get on a sitcom, man. I just want to get on a regular sitcom and I would be the happiest man on earth."

Referring to Matthew's substance abuse, he went on: "And watching that go on on the lot — we were at Warner Brothers, we were there right next to each other — it was hard to watch because we didn’t know what was going through him.

"We just knew that he wasn’t happy and I had no idea he was doing, what, 12 Vicodin a day and all the stuff he talked about, all that heartbreaking stuff. And it also just tells you that success and money and all those things, it doesn’t just automatically bring you happiness.

"You have to be happy with yourself and your life."

Matthew previously praised his co-stars on 'Friends' - including Jennifer Aniston, 54, Courteney Cox, 59, Lisa Kudrow, 60, David Schwimmer, 57, and Matt LeBlanc, 56 - for being "supportive" during his struggles.

He told PEOPLE of landing the role: "It changed my life in every way. I got the show when I was a 24-year-old man; the show ended when I was 34. It formed my life. And it was the time of my life."

Despite achieving his dream with 'Friends', Matthew wanted his legacy to be helping others through their addiction battles, and following his passing, a foundation was launched in his name to continue his efforts.