William Patrick Hitler was born in England to a German Father, Alois Hitler. His dad moved to Germany and when Adolf Hitler rose to power, he also moved, hoping to get a cushy job. His uncle agreed, but only in the condition that he renounce his British citizenship and promised never to go home.
He sensed something wasn't right, so he went back to England and wrote an article for Look Magazine called "Why I Hate my Uncle." This sparked a lecture tour through the US. They were in the US when WWII broke out and they were stranded.
He enlisted in the Navy with permission from President Roosevelt. He disappeared after the war. In 1998 it was found that he had changed his name to Stuart-Houston and died in 1987 with 4 sons in Long Island. Williams wife claimed her sons made a pact to never have children, as we talked about here.