Bryan Singer has revealed his next film -- and it's not an "X-Men" movie. On Instagram, the director marked his 50th birthday on Thursday with the news that he's finished the script for a "20,000 Leagues Under the Sea" film, based on the classic 1870 sci-fi novel by Jules Verne; declaring it his next film.

"A story I've wanted to retell since childhood," Singer wrote. "I promise this will be an epic and emotional adventure for all ages! An adventure very dear to my heart." Singer also made it clear he's "not abandoning" 20th Century Fox's X-Men films, saying he's very excited about "X-Men: Apocalypse" -- which he directed and is scheduled for release on May 27, 2016 -- "and beyond."

Deadline reports that the film isn't at a studio yet, but that Singer has shown the script to Fox -- though there might be a duel between studios for the project. As evidenced by the picture shared by Singer, he wrote the story with Rick Sordelet and Dan Studney, who are credited with the screenplay. Studney worked with Singer on 2013's "Jack the Giant Slayer."

"20,000 Leagues Under the Sea" has been adapted to film and television multiple times, most notably the 1954 live-action Disney film starring Kirk Douglas and James Mason. (The imagery used in this article is from a comic book adaptation of that film.) Here's Singer's Instagram post:

It's my 50th birthday (ouch), and I just put the finishing touches on the script for my next film. A story I've wanted to retell since childhood. I promise this will be an epic and emotional adventure for all ages! An adventure very dear to my heart. Not abandoning the #xmen universe. Very excited about #xmenapocalypse and beyond. #julesverne #20000leaguesunderthesea #nemo A photo posted by Bryan Singer (@bryanjaysinger) on