Will Butler’s time with Arcade Fire has come to a close. The instrumentalist, longtime member and brother to frontman Win Butler made his departure from the band public through Twitter on Saturday afternoon.

“Hi friends — I’ve left Arcade Fire,” Butler’s thread begins. “I left at the end of last year, after the new record was complete. There was no acute reason beyond that I’ve changed — and the band has changed — over the last almost 20 years. Time for new things.”

Butler also took space to memorialize Dr. Paul Farmer, founder of the health care nonprofit Partners in Health. Arcade Fire had been heavily involved in Partners in Health’s efforts over the past few years. Farmer died of a heart attack on Feb. 21.

“I’ll still be working with PLUS1 and Partners in Health — and the many activists and good humans and elected officials I’ve met — to give people material help; to build better systems of health, justice and government; to try to live up in some way to Paul’s example,” Butler continued.

As for future creative endeavors, Butler asserted that he is working on a new record, composing music for a play by David Adjmi and planning performances for the summer.

Butler joined Arcade Fire in late 2003 after multi-instrumentalist Brendan Reed departed from the group. Butler has contributed to every Arcade Fire album since its debut, 2004’s “Funeral.” He contributed to the group’s upcoming album, “The Lightning I, II,” which is set to release on May 6. Beyond Arcade Fire, Butler has released three solo albums.

“Thank you to anyone who’s come out to AF shows, or bought a record or loves our music. It’s meaningful to be part of your lives. Thank you to the crew, staff, management, label people, bands, artists and friends who have helped bring our vision to life for so many years,” Butler’s thread concludes. “I’ll be around! See you around!”