Christian II of Denmark was expelled from his kingdom by his uncle, lived in exile, and attempted to return to reclaim his throne.
However, his fleet was scattered by a storm off Norway and he ended up surrendering to Frederick, who kept him prisoner, albeit apparently comfortably, for 27 years.
What if his fleet avoided the storm and he landed with his followers in Denmark?
It seems Frederick (the uncle) was not a popular ruler, based on the peasant uprisings that took place and how Christian was viewed as a savior-figure.