Liam Payne 's girlfriend Kate Cassidy no doubt had people doing a double-take, as she rocked an eye-catching optical illusion dress in St.Tropez with her singer beau. The skintight blue patterned dress worn by the 24 year old American featured an apparent outline of breasts and torso, but it was simply the print on the dress. Elsewhere, the dress featured striking flower patters toward the bottom, as it clung to her figure whilst she walked.The stunning blonde accessorised with a pair of white court shoes and a small blue bag, whilst her hair was worn straight and her makeup was perfectly-applied.