I think it is referring to the titles of the close family members who held German titles such as the various members of the Battenberg clan, the Teck family, the daughters of Helena, and maybe some others. These people held German titles but were so closely associated with the British crown, even to the point of calling England home.
I believe at this time that George V also took the English titles from certain German relatives, such as the Coburgs and Hanovers.