Prince William, Princess Kate celebrate Tom Cruise at 'Digger' premiere in London

Prince William and Princess Kate were among the star-studded guests at the London premiere for Tom Cruise's new film, "Digger."

The Prince and Princess of Wales stepped out at the ODEON Luxe Leicester Square in central London on Tuesday for the premiere, alongside the film's stars and its director, Alejandro G. Iñárritu.

Kate wore a regal purple gown and accessorized the look with a heart-shaped necklace. The necklace, which appears to have pearls and an amethyst and diamond pendant, is reported to be the Queen Mother's Amethyst Sautoir Necklace, which was a gift from Queen Alexandra to Elizabeth Bowes-Lyon on her wedding day in 1923.

Kensington Palace did not share details about her look.

Queen Camilla appeared to have worn the same necklace in 2012 to the London premiere of "Skyfall."

Kate was all smiles as she arrived at the event with William by her side and mingled with Cruise and other filmmakers.

"Digger," out on Oct. 2 and filmed at Pinewood Studios near London, follows "the most powerful man in the world" who "embarks on a frantic mission to prove he is humanity's savior before the disaster he's unleashed destroys everything," according to a description of the film.

The cast includes Sandra Hüller, John Goodman, Michael Stuhlbarg, Riz Ahmed, Jesse Plemons, Sophie Wilde and Emma D'Arcy.

In a rare interview, Cruise spoke with GQ and said that "Digger" "is the culmination of all my skills. I’ve never done it before."

"Everything that I’ve done has been very thought-out, why I did it," he added. "I have personal goals and challenges with everything I do. I was so excited to be able to have this character. It’s the most challenging character ever.

Tune into "Good Morning America" from 7 a.m. to 9 a.m., ET on ABC on Wed., Sept. 23, for an interview with Tom Cruise about his highly anticipated film.