Here comes the bride, all dressed in… ?

Who Meghan Markle will be wearing when she exits her car in front of St George's Chapel at Windsor Castle on May 19 is the top mystery surrounding her upcoming wedding to Prince Harry.

If you check with the bookies, Paddy Power suspended bets as the company is "fairly sure" when Markle walks down the aisle she'll be wearing Ralph & Russo — again.

The London-based company led by Tamara Ralph and Michael Russo designed the sheer and beaded gown Markle wore for her engagement photos.

Celebrities favour the brand with a whimsical and high-glam aesthetic. Elizabeth Banks, Sofia Vergara, Heidi Klum, Alessandra Ambrosio and Rosie Huntington-Whiteley all wore Ralph & Russo designs to this year's Vanity Fair Oscar Party.

Experts agree Ralph & Russo is a top contender, followed closely by Erdem. Markle and Duchess Kate have both donned looks by Canadian-born designer Erdem.

Shelley Brown, fashion and beauty editor at The Knot, says Ralph & Russo is a "strong contender."

"The one I think might be most likely is Ralph & Russo, because obviously she’ll want to show the support for British fashion, and they’re a London-based luxury label that also has a couture label that already has a built-in bridal line," says Brown.

There's also speculation that Meghan will have a second wedding dress for the evening celebrations - as Kate, Duchess of Cambridge did for her wedding in 2011.