The daughter of Pivotal had a dream run around on the inside under Olivier Peslier, taking up the running with a furlong to run.
Unfortunately, her travel companion Ribbons was powering down the outside and got up inside the closing stages to win by two lengths.
A delighted Roger said: "Princess Loulou has run a terrific race. She has been placed in a listed race, a Group 3 and now a Group 1 so the main aim is to get her a stakes win.
"She is a lovely filly who is improving all the time. When she gets her ideal conditions she is up to winning a big one. We may bring her back to France for the Prix de l'Opera a race we won with Nahrain."
Princess Loulou (far side) finishes second to Ribbons