The iconic actress is lending her voice to Karathen, a mythical sea creature that will be helping Aquaman (Jason Momoa) broker a peace treaty between Atlantis and the land dwellers according to Variety.
Aquaman opens on Dec. 21, two days before the release of Mary Poppins Returns, when Blunt will take on a role originated by Andrews in the 1964 Disney classic (for which she won the Best Actress Oscar).
The news was first reported by Entertainment Weekly.
“We wanted the Karathen to have the voice of a classic British actress, albeit somewhat digitally altered,” Peter Safran, a producer on Aquaman, told the magazine. “And when we found out Julie was interested and available and excited to do it, casting her was a no-brainer.”
Aquaman will hit theaters in the U.S. on Dec. 21.