It was one of the bigger unexpected surprises from Microsoft's E3 press conference. During the show, it was revealed that the British developer Ninja Theory has been bought by Microsoft and now is a part of the Microsoft Game Studios team. Ninja Theory has mainly been working with Sony; Heavenly Sword was a PlayStation exclusive and Hellblade: Senua's Sacrifice didn't launch for Xbox One until recently.
On the other hand, the studio's very first game was Kung-Fu Chaos, which came out exclusively for the original Xbox back in 2003. So in that sense, the circle is complete with the team now getting back to Microsoft. Many have wondered why Ninja Theory wanted to make the move, and now they've posted a video where they explain everything.