Exclusive: Stars shine in 'Muppets' cameos

Tom Hiddleston, Celine Dion, Sean Combs, Lady Gaga, Zach Galifianakis — it seems everyone wanted to be in Muppets Most Wanted.

The film, which opened March 21, continued the Muppet tradition of great celebrity cameos. Who could forget Steve Martin as a surly waiter in 1979's The Muppet Movie?

"It's the blink-and-you'll-miss-it ones that are really fun," says writer-director James Bobin.

Some of appearances, such as getting Usher to play a wedding usher, are written into the script, says Bobin, while others just seem to happen spontaneously. For example, Bobin knew he needed Sean Combs for a Muppets celebration scene.

"If you're going to have a party," says Bobin, "P Diddy is the guy you want to have there."

Bobin was also aware that the Muppets have longtime actor fans like Christoph Waltz, who was called upon to dance a waltz. He jumped at the opportunity.

The quick scenes required the actors to rearrange their schedule to fit in the filming on the London set. Josh Groban was more than happy to make the trek for his scene in a Russian gulag.

"A Muppets cameo is a lifelong dream fulfilled. It was such a blast," says Groban. "I would have auditioned in Kermit boxers if I had to. Thank goodness I didn't have to."

Among the other actors who take a bow: Frank Langella, Tom Hollander, Hugh Bonneville, Ross Lynch, Stanley Tucci, Chloë Grace Moretz, Russell Tovey, Salma Hayek, Saoirse Ronan, James McAvoy and Tony Bennett.