Prince Harry and Meghan Markle's wedding is expected to be a royal wash out.

Prince Harry and Meghan Markle

Prince Harry and Meghan Markle

Pessimistic punters at online bookmaker Betfair have been heavily backing rain to be the order of the day when the happy couple tie the knot on Saturday May 19, 2018, with 90 per cent of bettors expecting Mother Nature to wreak havoc.

Betfair Spokesperson Katie Baylis told BANG Showbiz: "With all the speculation over dress designers, wedding guests, who will sing at the ceremony and all manner of other rumours doing the rounds, it's actually weather odds that are attracting the biggest number of bets on Betfair.

"Being a May wedding you would hope that we'll see a lovely sunny spring day for the couple, however punters are pessimistic with 90 per cent backing rain at odds at 13/8."

However, the odds are in Harry and Meghan's favour because Betfair go 4/9 that there will not be any rain dropping on St George's Chapel in Windsor Castle on the day of the pair's nuptials.

Speculation has been rife about Meghan's wedding dress designer in recent weeks and Alexander McQueen is thought to be the frontrunner after Betfair suspended betting on the outcome earlier this week.

McQueen was initially thought to be an outsider as a potential choice to design the garment before being heavily backed in the market this week.

The fashion house was a 16/1 longshot before the money started coming in and the price was slashed to 8/1, but a further flurry of bets led to the betting being suspended.