The character is adopted into a Wealthy family. If he is an orphan, it is a true adoption. If he has living parents, he is treated just like a son. (work with your DM to determine details)
In adulthood you have an encounter with an unusual person, who as far as you can tell, has no home or family. You offer to help in anyway you can. After accepting your hospitality the stranger vanishes leaving a note "Your kindness will be remembered".