The Bajan beauty has been romantically linked to the Kiss Kiss hitmaker for months, but both singers have continually denied they are a couple, despite being snapped in public kissing and cuddling.
The pair stepped up speculation about their relationship last week when they were snapped frolicking in a hot tub together in Los Angeles.
And now Rihanna has fuelled rumours that they are to walk down the aisle after she was snapped sporting a ring on her left hand.
The Toxic hitmaker has been accused of deliberately posing for photographers during a recent break in Cabo San Lucas - and taking a cut of the sale price.
According to New York gossip column PageSix, a photograph of her wearing a white bikini and swimming with dolphins was "set up by her camp".
But a spokesman for Spears has refuted the allegations.
The representative says, "If someone is trying to sell photos of Britney in Cabo, they're doing so without her knowledge or permission."
Source 1, Source 2