Sylvester Stallone unexpectedly popped in at the first preview performance of Broadway’s “Rocky,” based on his 1976 blockbuster film.

“Stallone made a surprise appearance at the end of the show and even stepped into the ring,” said a spy.

In the audience, Tom Hanks began chanting, “Rocky! Rocky!” and the crowd followed suit.

Also spotted were Hanks’ wife, Rita Wilson, and Paul Rudd. The trio headed backstage to congratulate Sly and the cast on a “knockout” performance.