In a surprising revelation, Kate Middleton had to undergo a fertility test to marry Prince William in 2011, media reports said.

This was a part of the protocol followed since the prince had chosen a bride outside royalty.

The test was conducted to ensure whether the future queen could bear children was apparently among them.

The surprising claim has been made in a new book, 'Gilded Youth: An Intimate History of Growing Up in the Royal Family', in which author Tom Quinn revealed interesting facts about the royal marriage, as reported by Hello Magazine.

Talking about the odd practice, the author reportedly stated: "These are always carried out to ensure a future queen is able to have children. If Kate had not been fertile, there is little doubt the marriage would have been off."

The book claims Princess Diana had to go through the same medical tests before her wedding to Charles in 1981, as per the Hello Magazine report.

"Diana complained in a brief encounter with the present author that she had in all innocence thought her premarital check-ups had to do with general health, only realising later on that she had actually been tested for fertility. 'I was so innocent I just went along with everything at that stage,' she said."

Prince William married Kate Middleton on April 29, 2011, in a grand ceremony at Westminster Abbey in London. Around 1,900 guests attended the wedding, for which a special eight-tier cake was commissioned and a public holiday declared in the country.

The royal couple is parents to  three young children - Prince George, Princess Charlotte, and Prince Louis.