[quote=@HueMan]I was toying with an idea about a nobleman's child who had been brought into the royal family to become a playmate for a young prince/princess (apparently this happened fairly often in history) but fell out of favor of the king as he/she grew up for some reason. Hence, the "former" noble. Of course, I'll flesh this idea out once you approve of the concept. 
[/quote]

Seems interesting. I believe that the main reason this kind of thing happened in history was to hold a noble's children hostage to their good behavior, so maybe your character's parents revolted / did something otherwise treasonous that caused your general dynasty to fall out of favor.

[quote=@Carantathraiel]
[@HueMan] a whipping boy!
[/quote]

There is also this option! Although then you'd probably be a peasant taken into the household specifically to be beaten when the prince/princess acts up, not a noble.