The actor's rep tells TMZ ... JMT passed away peacefully Sunday morning at his home in L.A. -- this after battling stage 4 prostate cancer.

His family says ... "The world knew him as Gunther (the seventh "Friend"), from the hit series "Friends," but Michael’s loved ones knew him as an actor, musician, cancer-awareness advocate, and loving husband."

They add, "Michael loved live music, cheering on his Clemson Tigers, and would often find himself in fun and unplanned adventures. If you met him once you made a friend for life."

James first revealed his cancer diagnosis earlier this year -- which stunned fans, as he'd just appeared in the reunion special and made no mention of it. He later clarified why he hadn't gone public at that time -- saying he didn't wanna be a downer for the special moment.

He was first diagnosed with cancer in 2018, and kept it private for 3 years.

James has acted in several big shows over the course of his career -- including "Sabrina the Teenage Witch," "Scrubs," "Modern Music," "Just Shoot Me!" and others ... but his biggest claim to fame is the long-running sitcom, where he played a worker at the Central Perk cafe.

He starred in 150 episodes of "Friends" over the course of its 10-year run ... and is absolutely beloved by the fan base. James is survived by his wife, Jennifer Carno.

James Michael Tyler was 59.