John Phillips, cofounder of the ‘60s folk rock group The Mamas and the Papas, died of heart failure at a Los Angeles hospital on Sunday morning (3/18) at the age of 65.

The Rock and Roll Hall of Famer was the band's chief songwriter, penning such hits as "I Saw Her Again Last Night," "California Dreamin'" and the Grammy-winning "Monday, Monday."

Phillips also penned the 1967 Scott McKenzie hit "San Francisco (Be Sure To Wear Flowers In Your Hair)," the Beach Boys' 1988 #1 hit "Kokomo" and the Grateful Dead's "Me And My Uncle." And along with Lou Adler, he staged the seminal 1967 Monterey International Pop Festival, which featured Jimi Hendrix, Otis Redding, Simon and Garfunkel, The Who, Ravi Shankar and Janis Joplin.

The Mamas and the Papas, which featured Phillips' then-wife Michelle Phillips, Denny Doherty and Cass Elliot, were a notoriously stormy quartet. They formed in 1964, broke up in '68, reformed in '70 and splintered for good in '71. They were inducted into the Rock and Roll Hall of Fame in 1998.

Until kicking the habit in the ‘80s, following a court-ordered rehab stint, Phillips had a long history of substance abuse. Like fellow ‘60s folk-rock legend/substance abuser David Crosby, Phillips had received a liver transplant in 1992, although he beat Crosby to the punch by two years.

Phillips is the second member of the group to pass away. Mama Cass Elliot died of a heart attack in 1974.

Just before entering the hospital, Phillips had finished a new solo album, "Slow Starter," and completed a record he started over 25 years ago with Mick Jagger and Keith Richards of the Rolling Stones, entitled "Pay Pack and Follow," which was due for a May release.

Phillips is survived by his widow Farnaz; his daughters Mackenzie, Chynna and Bijou; and his sons Jeffrey and Tamerlane.