Punters are already taking more of a gamble on Harry and Meghan's impending arrival than on the Duke and Duchess of Cambridge's first child, Prince George.
According to bookmaker William Hill, the turnover for Harry and Meghan's baby - who will be seventh in line to the throne - is up 80% compared with the run-up to the birth of future king George.
Most bets are placed immediately before a royal youngster's arrival, but bookies expect the trend to continue.
Rupert Hill, of William Hill, said: "Royal baby betting has never been more popular and the public clearly love Harry and Meghan.
"At this stage we think turnover will be higher for the Sussex baby than it was for Prince George."
He added: "The killer blow for the bookies is for the baby to be a girl and for them to choose to call her Diana."
William Hill has the arrival of a girl at odds of 8/11 and a boy at 1/1, while the name Diana - after Harry's late mother Diana, Princess of Wales - is 10/1, followed by Alice at 12/1, Victoria 14/1 and Alexandra and Elizabeth at 16/1.
For a boy, William Hill's favourite is Arthur at 12/1, followed by Edward, James and Philip all at 16/1 and Alexander at 20/1.
Outside odds include Albus after Hogwarts headmaster Albus Dumbledore from the Harry Potter books at 500/1, or Ginger in tribute to Harry's red hair, also at 500/1.
Paddy Power is facing a big payout if the couple have a girl and call her Diana.
Amy Jones, of Paddy Power, said: "We have seen continued support for Diana and it will be a five-figure pay-out for Paddy Power if that is the chosen name.
"Currently the 8/1 favourite, it has remained the favourite since we started taking bets on it."
Bookmakers also fear that Meghan will give birth to two babies instead of one.
Jones added: "Our biggest loser across all markets is Meghan to give birth to twins in 2019.
"We opened the price up at 33/1 back in October, and it's now as short as 2/1, and still continues to see support.
"So we'll be very nervous if this one lands."
The baby's weight is also the subject of speculation, with between 7lb and 7lb 15oz, and 8lb and 8lb 15oz the joint favourites at 2/1 with Paddy Power.
Odds that Meghan will give birth to a 10lb-plus baby are 16/1.
Harry was 6lb 14oz when he was born on September 15 1984.
Prince Louis of Cambridge weighed 8lb 7oz - heavier than both George, who was 8lb 6oz, and Princess Charlotte, who was 8lb 3oz.
But the heaviest royal baby in recent years is Zara and Mike Tindall's youngest daughter Lena, who weighed 9lb 3oz when she was born in June 2018.
The average weight of a baby in the UK is around 7lb 7oz.