"When people would ask us who a 'dream guest star' for the show would be, we would always joke and say Stephen Hawking -- knowing that it was a long shot of astronomical proportions," Executive Producer Bill Prady said in a statement. "In fact, we're not exactly sure how we got him. It's the kind of mystery that could only be understood by, say, a Stephen Hawking."
The episode is to air April 5.
Currently in its fifth season, "The Big Bang Theory" stars Jim Parsons and Johnny Galecki as Sheldon and Leonard, a pair of brilliant physicists whose lives are turned upside down when a free-spirited beauty, played by Kaley Cuoco, moves in next door.