Fans believe Meghan Markle has dropped a big clue about the Royal Baby's due date

Prince Harry and Meghan Markle announced on arrival in Australia they're expecting their first child together in 2019.

While some thought the Duchess of Sussex was 13 weeks along when the announcement was made, it was later suggested she may be further along into her pregnancy and would give birth in March.

However, eagle-eyed fans have spotted a clue to the Royal Baby's due date in one of the 37-year-old's outfits.

According to Royal fan, who tweets as Duchy of Success, the ring stack Meghan wore at an Invictus Games event on Cockatoo Island in Sydney, suggests baby Sussex is in fact due in April.

Here's the rational: the ring stack featured three colours, two of which are believed to represent Harry and Meghan's birthday months, which leaves one to signal their newest member of the family.

"I'm hoping Meghan’s stacked rings represent their birthstones and Baby Sussex is an April baby," the fan theorised.

"Meghan’s birthstone-green peridot," they noted for her August birthday, while Prince Harry's September date means his "birthstone-blue sapphire".

This leaves "Baby Sussex birthstone-diamond" they noted and others seemed to agree in the comments below.

Shortly after the couple announced their impending arrival an insider revealed Meghan had already undergone her 12 week scan the week before the news was made public and was "feeling well".

However, Australian singer Missy Higgins, spoke about the Duchess being four months along when they met in at an event on the Royal Tour, leading to speculation the mum-to-be was due sooner than expected.

The couple will most likely keep the exact due date tightly under wraps, as they will with the baby's gender - like Prince William and Kate have done in the past.