Eventually, Viola (still disguised as Cesario) and Orsino make their way to Olivia’s house, where Orsino thanks him for his deeds.
Olivia welcomes Cesario as her new husband, thinking him to be Sebastian, whom she has just married. Orsino then gets furious at Cesario for betraying him.
Sebastian then walks out an all is revealed, that Cesario is actually Viola.