Leonard Nimoy
Leonard Nimoy

Star Trek's very own Mr. Spock LEONARD NIMOY does the unthinkable!

Nimoy, 80, who announced his retirement from acting last year after completing his turn as other worldly mad doc William Bell on Fox's Fringe  has pulled the old switcheroo!

He's back to acting!

Nimoy has joined the cast of new Transformers: Dark Side of the Moon flick as the voice of Sentinel Prime, the predecessor of Optimus Prime.

Sentinel Prime's wrecked body appears in the new  teaser trailer, discovered by Apollo 11 astronauts on the moon in 1969.

Yet, Leonard is no stranger to the Transformers canon – he voiced Galvatron in 1986's The Transformers: The Movie.

In THAT film, Optimus Prime was thesped by the legendary Orson Welles.

Director and king of the exploding summer tentpole Michael Bay revealed how he lured the taciturn Vulcan thesp back to the robots-in-disguise fold.

"He's married to Susan Bay, who's a cousin of mine," Bay divulged.