The prefix Fitz- is an old word for "son of", especially used for the illegitimate sons of royalty. Bear that in mind as we lay out this factoid.
We recently came across this exciting book, A Descriptive Catalogue of the manuscripts in the Fitzwilliam Museum, by Montague Rhodes James (yeah, that M. R. James). The Fitzwilliam Museum is the art and antiquities museum of the University of Cambridge and was founded in 1816 with the bequest of the library and art collection of the 7th Viscount FitzWilliam.