Marvel licensed the filming rights of the X-Men and related concepts, such as mutants, to 20th Century Fox, who created a film series based on the franchise. Years later, Marvel started their own film franchise, known as the Marvel Cinematic Universe (MCU), which focused on characters that they had not licensed to other studios (see below). At the time, the rights to Quicksilver and Scarlet Witch were disputed by both studios. As they both held the rights to the characters, with Fox citing the characters' mutant status and being children of Magneto and Marvel citing the twins' editorial history being more closely tied to the Avengers rather than the X-Men, the studios made an agreement wherein both of them could use the characters on the condition that the plots did not make reference to the other studio's properties (i.e. the Fox films could not mention the twins as members of the Avengers while the MCU could not mention them as mutants or children of Magneto).[215] The arrangement became moot following the acquisition of 21st Century Fox by Disney – the parent company of Marvel Studios, and the confirmation that future X-Men films will take place within the MCU.