Actor James Darren, best known for his roles in Gidget and TV shows like T.J. Hooker and Star Trek: Deep Space Nine, has passed away at the age of 88.

According to TMZ, the beloved actor died peacefully in his sleep at Cedars-Sinai Hospital in Los Angeles on Monday.

While the cause of death is currently unknown, Darren’s son, Jim Moret, shared with TMZ that his father had been dealing with heart issues and had been admitted to the hospital’s cardiac unit.

Reports suggest that Darren had originally been hospitalized for an aortic valve replacement surgery, but doctors determined he was too weak to undergo the procedure safely. He was sent home but returned to the hospital shortly after.

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

Darren rose to fame as a teen idol when he played the role of surfer Moondoggie in the 1959 film Gidget, later reprising the role in its two sequels, Gidget Goes Hawaiian and Gidget Goes to Rome.

He also had a recurring role as Officer Jim Corrigan on T.J. Hooker, appearing in 66 episodes across four seasons. In addition to his acting career, Darren enjoyed success as a singer, famously performing the theme song for Gidget. He also directed several episodes of popular TV shows like Melrose Place, Beverly Hills, 90210, and The A-Team.

Rest in peace, James Darren.

Rest in peace, James Darren.