The pair were claimed to have 'enjoyed a string of dates' during their recent getaways in Dubai - where Kate had ventured with a bevy of girlfriends.
But the revealing nature of the dress didn't end there, and Billie, who is often known for ensuring she follows the best of the fashion trends, also opted for a low-cut back.
She was first romantically linked to Rio back in January, but the duo have apparently gone to great lengths to keep their 'romance' under wraps.