You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: PAINTERS 
Clue: His grandson was the cinematographer of "Barbarella" & "The Spy Who Loved Me"
pierre auguste renoir

Category: EUROPEAN PRINCESSES 
Clue: On July 20, 1999 she gave birth to her fourth child, Princess Alexandra of Hanover
princess caroline of monaco

Category: PHRASE ORIGINS 
Clue: This 2-word phrase may be traced to a line in a Sherlock Holmes story, "The chaplain stood with a... pistol in his hand"

smoking gun