This isn't the first and only case - in June, Coral slashed the odds on Prince Harry and Meghan welcoming a sibling for Baby Sussex.
"We have been inundated over the last few days with bets on Harry and Meghan having a second baby in 2020," spokesperson John Hill told The Mirror.
"And, as always with gambles of this kind, there is seldom smoke without fire."
That being said, Nicholl believes the rumours may be premature, as the royal couple appears to be focusing their attentions on baby Archie for the time being.
"They absolutely want siblings for Archie, so possibly we will have a pregnancy announcement -- a second pregnancy announcement for Meghan and Harry sometime next year -- but, for the moment, the focus is obviously on Archie," she continues.
Last month, a source told Express.co.uk that Prince Harry, in particular, is fiercely protective of Archie.
"He’ll basically protect Archie with his life," the royal insider stated.
The Duke and Duchess of Sussex faced public criticism after announcing that baby Archie’s christening on July 6 would be a private affair, however, the strong-willed couple is determined to keep their newborn out of the public eye as much as possible.
"Harry knew he would get it in the neck for not inviting the cameras in but he put Archie first – what father wouldn’t?" the source said.
"He just wants the best for Archie."