Churchill said it in 1943 after Nazi Germany surrendered in North Africa.
Actually it’s a very old saying. Machiavelli said something similar in the early 16th century: „They are proud and overbearing in victory, humble and fearful in defeat“.
But he was referring to the French.😀
There are some very nasty sayings about the English, and, dare I say it, about Americans, going around in mainland Europe. Still, I shall refrain from quoting any of them, as they are in no way conducive to a serious discussion.