You are mistaken for the missing offspring of the ruler of the land and are taken to live in the ruler's household. After 1d6 years something happens that causes you to leave. (work with your DM to determine details).
Divorce: During your adolescence your parents split up and you were forced to chose which parent to live with (Work with your DM to detirmine the details)
As an adult you joined a rebellion against the local ruler, if successful you are outlawed, if it failed you escape, with only friends and family knowing your involvement. (Work with your DM to detirmine the details)