Originally Posted by Old Pedant
(Have to admit I don't know where George V came up with the name "Windsor" other than, presumably, from Windsor Castle. Did it ever have any actual royal associations before that?)
My understanding is that it was from Windsor castle. The name schange was needed in a hurry to get rid of the German surname that Victoria acquired for the family when she married Albert - given that George had just gone to war with his German cousin.