There's a far cry between
disowned and
disgraced. Geo. II was referring to the fact that the rest of Europe might have seen Cumberland's peace as
disgraceful in the sense of it was not how war was done in those days.
Disowned is what most of the Hannoverians would've liked to do with their eldest sons - think George II, Poor Fred, George IV (even Victoria did it with Ed.VII). And I second what Constantine said above - Geo. II was looking for a way to leave Britain ("the devil take this island, as long as I can get out of it to return to Hannover") to his less-favored son, Fred, and his beloved Hannover to his favored son, William. Unfortunately, Parliament replied that such a move was not optional since the crown of Britain was not a personal possession of the king (as perhaps Hannover was) and could not be "assigned" in a will and testament.
Also, Geo. II's problem was compounded when Fred was killed by a cricket ball in attempts to appear wholly English

. His son was a minor - thereby requiring a regency, and England didn't exactly have the tradition of naming mother's regent, but rather the uncles exercised the power on behalf of the young king. So, he created a situation whereby, in the event of a regency for the young Geo. III, the Dowager Princess of Wales (Auguste of Saxe-Gotha-Altenburg) would
share her power of regency with Cumberland.
And if Cumberland were to be ruling his own country at that point, Parliament would hardly be more likely to let
him be regent, any more than they would've allowed D. Felipe II of Spain any say in the regency of a child he had by Mary. Because while 18c Hannover and 16c Spain are not really equatable, it's more the principle of a foreign king meddling in the politics to run the English kingdom.