Oscar winner Julie Andrews will appear in 'Aquaman' The renowned actress will play "an undersea creature."

Critically acclaimed, Oscar-award winning actor Julie Andrews will star in upcoming Warner Bros. film, "Aquaman," which is set to hit theaters on December 21.

Andrews will play Karathen, “an undersea creature that holds the key to Arthur Curry’s (Jason Momoa) quest to unite the Atlantean and surface worlds,” according to Entertainment Weekly.

"We wanted the Karathen to have the voice of a classic British actress, albeit somewhat digitally-altered," the film's producer Peter Safran told EW. “And when we found out Julie was interested and available and excited to do it, casting her was a no-brainer.”

The film’s director also tweeted the news, writing, "The most powerful creature on Earth is a dame," referencing Andrews.

The film is set to release next month during the same week as "Mary Poppins Returns."

Andrews won an Oscar in 1965 for playing Mary Poppins.