John Travolta Surprises as Danny Zuko at 'Grease' Sing-Along!

John Travolta made it a summer night out Friday at the "Grease" sing-along, surprising everyone by showing up — in full costume! — as his iconic character Danny Zuko.

It was a real case of, "Look at me, I'm Danny Z!" as he joined castmates Didi Conn, Barry Pearl, Kelly Ward, Michael Tucci and director Randal Kleiser.

After, the 71-year-old superstar posted a photo of himself on Instagram in his black leather jacket and a pompadour wig, announcing, "Tonight at the Hollywood Bowl, for the first time I surprised everyone at the GREASE Sing-A-Long and dressed up as Danny Zuko. No one knew. Not even the cast. Thank you for a great evening."

He also shared a video of his shocking arrival at the event, which had the crowd going wild for the one that they want. "I thought you were goin' back to Australia?" he teased, referencing a plot point involving Sandy, played by the late Olivia Newton-John. "That's cool, that's cool, baby. You know — rockin' and rollin' and what-not."

He led the Bowl's lucky audience in a spirited, "A-womp-bomp-a-loom-bop, a-womp-bam-boom!" He wished the hopelessly devoted crowd a good show and parted with, "We love you!"

"Grease" was at one time the highest-grossing musical ever released, raking in $130M at the box office. It has become an undisputed film classic, frequently drawing large crowds at sing-alongs and other revivals, and inspiring 2016's televised "Grease Live!"