The girls sat front row at Jean Paul Gaultier and, while Katy was gorgeous in a black halterneck dress and Louboutin heels, all eyes were on Rihanna as she worked a cut-out coat with a strappy bustier top.
She teamed the daring look with electric-blue bandage booties and PVC trousers.
Rihanna and Katy became close after going on holiday to Barbados together in April.
Katy, 24, joined the Umbrella star in her home country for a beach break, which saw them soak up the sun and enjoy speedboat rides.
And the singer described Rihanna as a ‘cool chick’, adding: ‘We're friends and we're both kind of on this crazy roller coaster, and... it's nice to have good girlfriends.’