Katie wows Batman fans
The stunning gown - reportedly a gift from 42-year-old boyfriend Tom Cruise - sparkled with £10,000 of Swarovski crystals.
The pretty 26-year-old, who plays the caped crusader's childhood sweetheart in the movie, coyly refused to reveal if she and the hunky 'War of the Worlds' star are engaged.
She said: "Being in love with Tom is amazing and I love him very, very much.
"At the moment we're just both very busy loving, being in love."
But the sexy actress confessed: "But it does make me smile to think about it."
The former 'Dawson's Creek' star was joined at the premiere by co-stars Christian Bale, Morgan Freeman and Sir Michael Caine - and not least, the Batmobile.
Meanwhile, Katie is reportedly taking lessons in Scientology sparking further speculation she is set to marry Tom - a longtime supporter of the religious group.
She admitted: "I have been taking some courses and I really like it."