Paddy Power claimed the flurry of bets placed on the Duke and Duchess of Sussex already having welcomed a baby girl overnight suggested "someone knows something".
Doria Ragland, Meghan's mum, arrived in the UK on April 26 in sign that her daughter was about to give birth.
Prince Harry and Meghan Markle referred to their child as "Baby Sussex" for the first time on April 15, sending royal fans into "meltdown", according to reports.
The couple used the term while thanking well-wishers on their official Instagram page for donating to charities for children and parents, instead of sending them gifts.
The soon-to-be parents wrote: "On behalf of The Duke and Duchess (and Baby Sussex), we thank you so much."
This comment prompted one royal fan to respond: "I think this is a great way to communicate. And mentioning Baby Sussex is the cherry on top!"
On a trip to Birkenhead, Meghan confirmed that she does not know the royal baby's gender as she and Harry want it to be a surprise.
The 37-year-old revealed she was six months' pregnant as she met locals in the Merseyside town during her and Prince Harry's first joint engagement of 2019 on January 14.
Buckingham Palace announced that Meghan and Harry will keep the birth of their first-born private until they have had an opportunity to celebrate as a family.
In a statement, the palace said: "The Duke and Duchess of Sussex are very grateful for the goodwill they have received from people throughout the United Kingdom and around the world as they prepare to welcome their baby.
"Their Royal Highnesses have taken a personal decision to keep the plans around the arrival of their baby private.
"The Duke and Duchess look forward to sharing the exciting news with everyone once they have had an opportunity to celebrate privately as a new family."
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