The Los Angeles-based five-piece completed its first international tour late last year (11), but now Rathbone and his bandmate, fellow actor/musician Jerad Anderson, have walked away from the group to focus on other projects.
A statement on the band's website reads: "Hey folks, 100 Monkeys has some news. Due to demands on their personal lives and professional careers, our good friends Jackson Rathbone and Jerad Anderson will be leaving the band as active members.
"We have much love for both and wish them well, and they will always be welcome if they should ever decide to drop in on any future shows, or make appearances on recordings... We wish them the best in their future projects and anticipate great new things to come."
Rathbone and his girlfriend Sheila Hafsadi announced their baby news last month (Feb12).