In a twitter post on Thursday, Sum 41 drummer Steve 'Stevo' Jocz announced he has quit the group after 17 years in the line-up.
The Screaming Bloody Murder rocker thanked fans for their support but failed to give details for his reason for his sudden departure.
He writes, "I'm sorry to announce that I've decided to leave Sum 41. Touring with the band has been an amazing experience that has taken us far beyond our old practice space in my parent's basement to countless countries around the world."
"I've had the opportunity to see and experience so much and for that I am truly grateful. I just want to thank all of our fans for making the last 17 years possible. I had a blast. Thanks again."
Jocz co-founded the Canadian punk group in Ajax, Ontario with his friend Deryck Whibley in 1996 and has played on all five of the group's studio albums.
Sum 41 is due to release a new record later this year.