kate middleton bikini photo

Kate Middleton bikini photo. SolarPix, PacificCoastNews.com

This Kate Middleton bikini photo leaves no doubt whether she's "fit" to be royal.

Never mind all the speculation on which designer she will be wearing for her April 29 nuptials. Great Britain's future Princess of Wales has slipped on something white before, according to this bikini look, far sexier than the covered-up one she's expected to wear when she weds Prince William.

The queen-to-be is sparking a bit of a tabloid frenzy today with the surfacing of these "never before seen" photos, circa 2006, of her tanned and taut self sunning on a yacht off the coast of Ibiza, Spain.

Middleton was vacationing with Prince William when she was photographed wearing this sexy, halter-style white bikini, which showed off an impressively flat set of abdominals.

Professional Kate-watchers attribute Middleton's six-pack to regular workouts at the Clarence House sports club in London and beauty treatments at Richard Ward Hair and Metrospa in London's tony Sloane Square.

StyleList is just happy to see the royal fiancée photographed wearing something besides her smart, if predictable flat, black suede boots, which we hear are the product of American brand Aquatalia by Marvin K.

Meanwhile, read about the sheer, sexy dress Middleton wore when she first met Prince William. The flimsy frock is set to hit the auction block this week.

And check out our gallery of celebs flaunting their bikini bodies.