Microsoft has backed “Fortnite” video game maker Epic Games in its legal battle with Apple – alleging in a new court filing that the Tim Cook-led tech giant has “stymied” its own efforts to create an Xbox mobile store.

Microsoft says Apple's App Store rules are to blame for the continued delay of the Xbox mobile app store it announced last summer. In an amicus brief filed this week first spotted by The Verge, Microsoft expressed support for Epic Games in the company's long-running bout against Apple.

Now that Fortnite is back on iOS with Apple's approval of the game, Microsoft is jumping in to try to extend its ability to sell games on the platform through its Xbox app.Microsoft on Tuesday filed an amicus brief in district court in support of Fortnite publisher Epic Games saying that Apple has "stymied" its efforts to sell games through its mobile Xbox app on iOS.