Matthew Perry Says Past Substance Abuse Has Caused Him to Forget '3 Years' of 'Friends'

The actor was battling personal demons while playing the role of a lifetime.

While playing the role of a lifetime, Matthew Perry was battling addiction.

During a recent interview on BBC Radio 2 in Britain, the 46-year-old actor found himself unable to recall his least favorite episode of Friends due to his admitted substance abuse at the time.

"I think the answer is I don't remember three years of it," he candidly admitted. "So none of those... somewhere between season three and six."

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This is not the first time Perry has opened up about his struggles with Vicodin and alcohol. In August, the actor gave a very candid interview with the Hollywood Reporter, where he explained, "You can't have a drug problem for 30 years and then expect to have it be solved in 28 days," adding, "Getting sober is a really hard thing to do."

In 2013, Perry -- who has been to rehab twice -- turned his former Malibu home into a sober living facility called Perry House.

WATCH: Matt LeBlanc and Lisa Kudrow Have a Super Sweet Friends Reunion at the 2015 Emmys

Meanwhile, the cast of Friends just celebrated a mini-reunion!

With the exception of Perry, whose rep told ET that he couldn't join due to a scheduling conflict -- the actor is currently preparing for his upcoming play, The End of Longing -- the whole gang got together over the weekend to participate in a tribute broadcast honoring legendary TV director James Burrows. It marked one of the rare appearances of our favorite Friends ever reuniting since the show went off the air in 2004.

Watch the video below.