Quote Originally Posted by YourLordandConqueror
If I can remember correctly, my family's name was anglicized to "Seymour" after the Norman Conquest.
The name Seymour is an Anglicised French-Norman name. It is derived from 'Saint-Maur', a town in Normandy. Its lord conquered England together with William the Conquerer.

Maybe you really can genealogically trace your ancestry back to Norman nobility. Maybe your family at one point adopted the name of Seymour. And much later somebody else in your family read up about the meaning of the surname and without further investigation accepted the 'Norman noble' family origin explanation, for all the glamour it brings.

Yes, my family was noble but slowly lost that status,
Actually, few noble families slowly lose their status. This usually means that somebody does genealogical research, discovers noble blood somewhere, and this later gets turned into a family legend. 'Once we were noblemen...'

There is probably not a single family in Europe without multiple infusions of noble blood. Such is the nature of genetic diffusion. You have two parents, four grandparents, eight...sixteen....thirty-two etcetera. Go back a thousand years, and you have 2^40 ancestors.
So you probably do have French-Norman ancestors. In fact, one would be hard pressed to find a single Briton without any.