Sadly, another castaway has left the island for good.

Russell Johnson, best known for playing the brainy Professor on Gilligan's Island, has died, E! News confirms. He was 89 and the last surviving male star from the classic 1960s sitcom—which famously listed all of its characters in the more well-known version of its iconic opening theme song.

We're told that the actor died of natural causes Thursday at 5:21 a.m. at his home with wife Constance and daughter Kim by his side.

"He was a gentleman, very kind," Johnson's agent, Mike Eisenstadt, tells E! "He was very smart and very respectful. He was a nice, normal guy."

Johnson retired from acting in the 1990s but still made Gilligan's Island-related appearances in more recent years.