X-Men: Days Of Future Past director Bryan Singer made good on a bet with his assistant after agreeing to get a tattoo if the film crossed the $700 million (Gbp422 million) mark at the global box office.

The latest X-Men movie opened in cinemas in May (14) to overwhelming success, raking in $110 million (Gbp69 million) in the U.S. in its debut weekend alone.

When the superhero film passed the $500 million (Gbp301.5 million) benchmark, Singer's assistant inked the official round X-Men symbol on his calf, and challenged his boss to do the same if and when the film passed $700 million.

Singer shared a photo of the new tattoo on Instagram.com last month (Jul14), and wrote, "My assistant kept his end of the bet. Tattoo at 500mil. Sucka (sic)! Yet now we are passed 700 it's (screenwriter Simon) Kinberg and my turn."

And on Wednesday (20Aug14), Singer made good on his wager, posting a photo of himself getting inked at Los Angeles' Shamrock Social Club tattoo parlour.

Offering moral support, Sir Patrick Stewart, who plays Professor X in the franchise, was on hand during the session to observe as the tattoo artist got to work on Singer's calf.

The director added the caption, "Getting my X-Tattoo with @sirpatstew witnessing midnight," while Stewart tweeted, "I'm great support staff."

The success of the film is a real tonic for Singer, who pulled out of promoting the movie after he was accused of sexually assaulting a teenager. The case has since been dismissed.