That sound suspiciously like Roald Dahl’s “Dip in the Pool.”
Winston Churchill wrote several best-selling novels; his “The Crisis” and “The Crossing” were massive best sellers. But it was Winston S. Churchill who became British PM, who included his middle initial in his byline to avoid confusion.
More seriously, Franklin D. Roosevelt is given story credit for The President’s Mystery. He really only gave the basic idea for the story (How could a millionaire disappear and start a new life for himself, under a new identity, and manage to take his wealth with him?), but he did have a credit on the screen.
Elizabeth I wrote sonnets, but, then, everyone in England in her time wrote sonnets.
Her father, Henry VIII, composed church music.