The royal baby due date is one of the most closely guarded secrets surrounding the Duchess of Cambridge’s pregnancy, said the MailOnline.

But last Sunday, the expected due date of the potential future leader of the United Kingdom was disclosed. July 13 is the official royal baby due date - the one given to the Duchess of Cambridge, according to The Mail.

Mystery has shrouded the expected date of birth ever since Kate was rushed into the King Edward VII hospital with severe morning sickness in December, early on during her pregnancy.

Because of Kate's illness, the Palace was forced to announce she was expecting before she had undergone her 12-week scan, which indicated that no one outside Kate and William’s close circle knew how far the pregnancy had progressed.

A friend of the pair revealed “some of Kate and William’s close pals were at a barbecue hosted by a family friend of the Royals recently.”

Friends at the party were all discussing the fact that Kate’s baby is due to be born on the 13th of July and everyone was excited for the royal baby due date.

Out of coincidence, the birth due date falls right in the middle of the Coronation Festival, a four-day celebration to mark 60 years since the Queen was crowned.

The festival is expected to rival last year’s jubilee celebrations and runs from July 11 to July 14 – meaning that the Prince and Duchess of Cambridge will miss out the celebrations.

The baby is expected to be delivered in the private Lindo Wing of St. Mary’s Hospital in Paddington – the same place were the Duke of Cambridge was born. Kate will be under the supervision of Royal gynaecologists Alan Farthing and Marcus Setchell.

As soon as the pregnancy was announced months ago, bookmakers began taking bets on whether the baby might share a birthday with Princess Diana on July 1.

Now that the royal baby's due date has been disclosed, it appears the birthday is closer to the Duchess of Cornwall's, on July 17. The MailOnline said that unless the baby is more than nine days late, it will be born under the same cancer star sign as Diana, who was an avid astrology follower.

Aside from one of the days in 2013’s coronation festival, the royal baby’s birthday falls under the same birth date of some notable individuals. Frida Kahlo, Harrison Ford and Julius Caesar were all born on July 13.

Proposed changes to the rule of succession mean that if the baby is a Princess, she will be third in line to the throne, even if she will have a younger brother in the near future.

According to a Palace spokesman, “We have only said that the Duchess is due in July. Anything further would be speculation.”