Basically it goes as follows:
1.) Ubisoft was making a sequel to Prince of Persia 2008 that got cancelled.
2.) The team started on Prince of Persia Zero, a series reboot which also got cancelled.
3.) Around the time of Prince of Persia Zero, Ubisoft also started a new IP called Osiris that was sort of like Shadow of the Colossus meets God of War in Egypt.
4.) Sometime after Prince of Persia Zero's cancellation, they tried to turn Osiris into Prince of Persia Zero 2.
5.) The transition didn't go well, so they turned Prince of Persia Zero 2 back into Osiris.
6.) Osiris was cancelled sometime after E3.
Or, you know, your average Ubisoft production timeline. This is how they have 8000 employees and so little major AAA output.