TOM CRUISE was so exhilarated on the first day of filming upcoming movie sequel MISSION: IMPOSSIBLE III he began singing the classic TV show's theme song midway through an action sequence.

The 43-year-old's impromptu a cappella performance left his co-star JONATHAN RHYS-MEYERS more than a little surprised.

Rhys-Meyers says, "The first day of shooting, Tom and I were on this speedboat. That was the first time I met him.

"The next thing I hear is him under his breath, 'Da-da-da-da-da-doodle-do.' He was so excited that he was humming the theme song.

"At first I thought they'd put the soundtrack on to give us more of a buzz. But it was Tom. Singing."