"It was a very lonely time for me." Matthew Perry went to rehab twice while filming Friends.

From the ages of 24 to 34, Matthew Perry seemingly had it all.

At the height of his fame, while starring as lovable underdog Chandler in Friends, he was one of the world’s most recognisable faces.

Watch the iconic Friends “pivot” scene. Post continues after.

But behind the scenes, despite his high pay cheque, the fame and the glamour of Hollywood stardom – he was battling drug and alcohol addiction, often showing up to set “painfully hungover”, and recently admitted that three years on the beloved sitcom are now just “a blur” to him.

The actor has been in and out of rehab since 1997 for addiction to prescription medication Vicodin and alcoholism. While in recent years, he's opened up about his struggles in interviews, on Twitter, and even launched his own rehab facility operating out of his home from 2013 to 2015, the 49-year-old actor was photographed in public for the first time in almost two years last week. His appearance has sparked concern amongst fans.

Wearing a tracksuit and t-shirt as he walked down the street, the images, which you can see here, have prompted fans to wonder whether he's fallen off the wagon.

But his response to the criticism has been priceless.

Following the Daily Mail publishing a paparazzi photo describing him as “dirty and unkempt”, Perry used his Twitter account to respond to particularly vicious comments about his "long fingernails."

Following it up with an iconic scene from Friends:

It's not the first time he's addressed concerns surrounding his health on Twitter.

In February, he posted that he had been kicked out of therapy, but later told his followers to not worry as “I’m back in therapy where I belong”.

Last year Perry was admitted to hospital with a ruptured bowel, spending three months recovering.

Fans had been worried about the absence of the actor, whose rep told ET in early August 2018 that Perry “recently underwent surgery in a Los Angeles hospital to repair a gastrointestinal perforation” and that the actor was “grateful for the concern and asks for continued privacy as he heals”.

Things started to go downhill for Perry after a jet ski accident in 1997, when he became addicted to Vicodin while treating his injuries.

“I felt better than I ever felt in my entire life. I had a big problem with pills and alcohol, and I couldn’t stop,” he told E Online in 2013.

He says the pressures from the success of Friends further fuelled his addiction, describing it as a "lonely time".

“I was in the white-hot flame of fame. The six of us were just everywhere all the time. From an outsider’s perspective, it would seem like I had it all. It was actually a very lonely time for me because I was suffering from alcoholism. It was going on before Friends, but it’s a progressive disease. I wasn’t a massive party guy. I wasn’t a bull-in-a-china-shop kind of drinker.”

He went to rehab multiple times, twice while Friends was still running. His first treatment was in 1997 while trying to kick his prescription pill habit, and second in 2001 to deal with his alcoholism.

According to People, he stayed at Minnesota’s Hazelden Foundation rehabilitation centre for 28 days.

“I don’t think there’s anything in the world that I can’t face, having faced that,” he told People. “That was the scariest thing that’s ever happened to me. You get a whole new respect for yourself and life when you go through something that difficult.”

In between his first and second trips to rehab, Perry was treated for acute pancreatitis and lost 20 pounds. He later attributed the condition to both alcohol abuse and prescription drug abuse.

“In my case, it was hard living and drinking hard and eating poorly,” he said. “You play, you pay. But there were no pills involved. I learned my lesson at Hazelden.”

As he revealed in a BBC interview in 2016, he can’t remember a large chunk of Friends because of his addiction. When asked what his least favourite episode was, Perry responded; “Oh, my goodness, I think the answer is, I don’t remember three years of it. So none of those… somewhere between season 3 and 6.”

Perry told People in 2013 his struggles were hard to mask while filming the show. “I couldn’t stop. Eventually, things got so bad that I couldn’t hide it, and then everybody knew.”

He spoke about his complicated relationship with the spotlight to the New York Times in 2002: “I was a guy who wanted to become famous… You want the attention, you want the bucks, and you want the best seat in the restaurant,” he said.

“It’s kind of like Disneyland…” he explained of the success that accompanied Friends. “For me it lasted about eight months, this feeling of ‘I’ve made it, I’m thrilled, there’s no problem in the world.’ And then you realise that it doesn’t accomplish anything and it’s certainly not filling any holes in your life.”

“I was never high at work,” he added.

“I was painfully hungover.”

Shortly after his release from hospital for pancreatitis treatment, Perry crashed his Porsche into an empty house. He escaped unscathed, and when searched, neither drugs nor alcohol were found in his system.

“The irony was terrible, it was an awful day,” he told People.

“I was going to hang with my father at his place outside L.A. I made the first corner around my house on these really narrow streets, saw a courier van in the middle, swerved to the right and—well, I don’t really know what happened—I crashed into this porch.”

Soon after, in 2011, he made a third trip to rehab, not after a relapse, but in an effort to be proactive.

“I’m making plans to go away for a month to focus on my sobriety and to continue my life in recovery,” he said. “Please enjoy making fun of me on the world wide web.”

Perry's Twitter presence has consistently remained a space in which he pokes fun at himself through the lens of the tabloids.

But aside from securing himself as one of the most entertaining celebrities to follow on social media, he's been committed to helping those recovering from drug and alcohol abuse by supporting drug and alcohol programs.

Speaking at the annual National Association of Drug Court Professionals conference in 2013, the actor said; “Drug courts are the single most effective program for curing serious drug addicts for lifelong recovery.”

Perry added, “Any opportunity I get to talk about drug courts on a one-on-one level or a much bigger level—like testifying in that scary room—I grab at because it’s just one of the few things that’s a no-brainer: it saves lives, it saves money, it’s bipartisan.”