Katie Holmes has been working round the clock to ensure she is ready to tread the boards for her Broadway stage debut in All My Sons.

The 29-year old has left behind husband Tom Cruise and daughter Suri in Hollywood as she prepares for her role in New York’s theatreland.

A source tells The Mail that cast members are in awe of her profession dedication: “She's doing anything up to 12 hour days.”

”It's the biggest role of her life and Tom is helping her every step of the way.”

"Tom plans on bringing Suri to New York as much as he can so they can all be together,” adds the source. “He'll be back and forth to L.A. He's working on stuff too.”

Katie will be onstage six nights a week, and will co-star along stage and screen veteran John Lithgow.

Will Britney be in the audience getting Broadway tips?