Actor James Darren, known for his work on films including Gidget and TV shows such as T.J. Hooker and Star Trek: Deep Space Nine, has died at the age of 88.

TMZ report that the veteran performer passed away in his sleep at Cedars-Sinai Hospital in Los Angeles on Monday.

Darren’s cause of death remains unknown a the time of writing, but the actor’s son, Jim Moret, reportedly told TMZ that his father was having heart issues and was a patient at Cedars-Sinai’ cardiac unit.

It’s believed that Darren had initially gone to hospital for an aortic valve replacement, only to be judged too weak to safely undergo the procedure.

He was subsequently sent home, but returned to hospital a short time later.

“I always thought he would pull through,” his son Jim said, “because he was so cool. He was always cool.”

Darren shot to prominence as a teen idol after landing the role of surfer Moondoggie in 1959’s Gidget. He reprised the role in the two sequels Gidget Goes Hawaiian and Gidget Goes to Rome.

The actor also had a recurring role as police officer Jim Corrigan on T.J. Hooker. He appeared in a total of 66 episodes across four seasons.

Beyond acting, James also enjoyed a career as a singer and performed the theme song for Gidget. As per reports, he also directed a variety of episodes on shows like Melrose Place, Beverly Hills, 90210 and The A-Team among others.