The hidden significance behind the official due date for royal baby number three.

Almost two months after we learned a third royal baby was on the way, Kensington Palace has officially confirmed when we will meet our next little Prince or Princess.

Sharing the announcement on Twitter, the Palace confirmed Prince William and the Duchess of Cambridge are expecting baby number three to arrive in April 2018.

The Duke and Duchess of Cambridge are delighted to confirm they are expecting a baby in April 2018. pic.twitter.com/jOzB1TJMof

— Kensington Palace (@KensingtonRoyal) October 17, 2017

Besides the fact that their family will now be one of five, the due date holds a special significance for Kate and Wills – they were married on April 29, 2011.

It’s also the same month Queen Elizabeth II will celebrate her 92nd birthday, and just one month later that the date Princess Charlotte was born.

As with her first two pregnancies, the 35-year-old has been suffering from Hyperemesis Gravidarum, a form of severe morning sickness, since learning she was expecting.

It wasn't until last week that the public got their first glimpse of the pregnant Duchess of Cambridge, who had not being attending public engagements while she sought treatment. She was even forced to miss Prince George's (adorable) first day of school.

To see Kate Middleton's maternity style CLICK THROUGH the gallery. Post continues... 

While the couple's announcement that they were expecting another child came as a shock to many, there had been a few hints that another baby was on the way.

During their European tour earlier this year, Kate made a light-hearted joke to husband William when she was gifted a soft toy for newborns.

"We will just have to have more babies," she joked, proving that the couple may have already been relishing in the fact that baby number three - who will be fifth in line to the British throne when it is born - was on the way.

LISTEN: Mamamia Out Loud on the 'strategic' dress codes of Kate and Wills.