James Darren, the beloved actor known for his roles in classic films like Gidget and TV series such as T.J. Hooker and Star Trek: Deep Space Nine, has passed away at 88. TMZ reports Darren died peacefully in his sleep at Cedars-Sinai Hospital in Los Angeles on Monday.

While the exact cause remains unclear, Darren’s son, Jim Moret, told TMZ that Darren had been experiencing heart problems and was under care in the hospital’s cardiac unit. Initially, Darren went to the hospital for an aortic valve replacement, but doctors decided he wasn’t strong enough for the surgery. After being sent home, he was later rehospitalized.

“I always thought he’d pull through,” his son Jim fondly recalled, “because he was always so cool.”

James Darren rose to fame as Moondoggie in the 1959 hit Gidget, reprising the role in sequels Gidget Goes Hawaiian and Gidget Goes to Rome. He also starred as Officer Jim Corrigan in T.J. Hooker and enjoyed a successful directing and musical career. Rest in peace, James.