The 2011 Assassin's Creed game starring Ezio and featuring Altaïr's story is Assassin's Creed: Revelations.
Revelations is the fourth major installment in the series and was released in November 2011. It follows an older Ezio Auditore as he travels to Constantinople, where he searches for keys connected to Altaïr Ibn-La'Ahad's former headquarters in Masyaf.
The game uses a framing structure that connects the two protagonists. Players control Ezio for most of the campaign, while playable sequences show important moments from Altaïr's later life. The story also continues Desmond Miles' modern-day narrative.
The title is often confused with Brotherhood because both games star Ezio. Brotherhood is set primarily in Rome and focuses on Ezio's campaign against the Borgias. Revelations instead centers on Constantinople and serves as a concluding chapter for Ezio's main trilogy. Its setting reflects the historical city known today as Istanbul.