The 'Don't Be Afraid of the Dark' star admires the styling of Catherine Middleton - who became a duchess in April when she married Prince William, the second in line to the English throne - as well the way her sister, Pippa, dresses.
Speaking at the film's premiere in Los Angeles on Sunday (26.06.11), Katie told Usmagazine.com: "I love both Kate's and Pippa's style and I think they are incredible. I'm so happy for Kate - I wish them the best!"
The 32-year-old star was also full of praise for her husband, Tom Cruise, whom she revealed is newly buff for his role as tattooed musician Stacee Jaxx in 'Rock of Ages'.
She said: "His body looks great and I'm so excited for him playing this character.
It is also possible Katie and Tom may get to meet the duke and duchess, through their mutual friends David and Victoria Beckham.
The royal couple invited the Beckhams to their wedding and are likely to meet with them in coming weeks when their first royal tour together makes a stop in California, and the Beckhams are sure to be keen to introduce them to some of their close friends.