The cast of the big-screen 'Mamma Mia!' – from Meryl Streep and Pierce Brosnan to Colin Firth, Stellan Skarsgard and Amanda Seyfried -- assembled at New York's Ziegfeld Theatre Wednesday night to premiere their ABBA-tastic musical -- and ET was there!

"It's [like] a Grecian night, so beautiful," Meryl told us on the blue carpet. In the movie, she does a cannonball jump into the water off of a dock, and when we told her that our own Jann Carl and Lara Spencer did the same thing, she exclaimed, "Did they really? Those girls are game! It was hot. [Over there] we discover our inner kids."

"This movie's got such heart," said Pierce, adding, "We became a family, these eight people that were in this movie. This is great entertainment."

And Amanda told us, "'Mamma Mia!' is my favorite [ABBA} song hands down -- I mean, my heart pounds [when I hear it]."

In theaters everywhere Friday, 'Mamma Mia!' follows an independent, single mother (Meryl) and her spirited, about-to-be-married daughter (Amanda) who is determined to find out the identity of her father so that he can walk her down the aisle. Pierce, Colin and Stellan's characters were all involved with Meryl's character 20 years earlier when they visited her Greek paradise, and any one of them could be the father!

Inspired by the incredibly catchy music of ABBA and based on the hit musical that toured the world, 'Mamma Mia!' features such sing-along classics as "Dancing Queen," "Knowing Me, Knowing You," "SOS" and "The Winner Takes It All."