that's right - 'same middle name' is the usual answer. As the latter's name is usually just 'Rupert Bear', the question often specifies Winnie the Pooh or William the Conqueror.
Apparently two thirds of the worlds modern day population are at least partially decended from Attila the Hun. Recent genetic research has found that not only Rupert but also Bill the Badger, Andy Pandy, Bob the Builder, The Pink Power ranger, Tiny Clanger and Ken Livingstone all share this same famous relative.