British royal house (7)
'british royal house' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for windsor that I've seen before include "Berkshire castle" , "Family name replacing Saxe-Coburg-Gotha in 1917" , "Home to Shakespeare's merry wives" , "former German house?" , "Thames town" .)
(Other definitions for hanover that I've seen before include "German 22 Across" , "Royal house of Britain 1714-1901" , "Victoria's House" , "British royal house, 1714 to 1901" , "British dynasty" .)