The shocking thing Grace Kelly had to prove before her royal wedding

Grace Kelly became one of the most iconic royals in the world when she married Prince Rainier II of Monaco after years as an American film star.

Their romance seemed to be one from a fairy tale, where the Hollywood beauty fell for the European prince and they wed in a lavish ceremony.

But behind the scenes in the lead up to their wedding, Grace was allegedly forced to submit to two shocking demands from the Monegasque royal family.

The then-26-year-old reportedly had to prove that she could provide royal heirs by submitting a fertility test to the royals, according to the Chicago Tribune.

Being able to have children was – and still often is – an important thing for a royal couple, as it secures the royal bloodline and ensures the family will be able to continue ruling for generations to come.

Even when Prince William and Kate Middleton wed in 2011, there was talk about how quickly the Duchess would fall pregnant and give birth to the next Windsor.

While we're sure the Queen was eager to add another great-grandchild to her Christmas gift list, it's unlikely she'd ever ask a woman to provide a fertility test before marrying into the British monarchy.

But 1956 was a different time, and Grace is believed to have provided proof of her fertility before her wedding to Prince Rainier.

However, that wasn't the only thing she had to do in the leadup to her nuptials.

Grace was also allegedly told her father would have to pay a $2 million dowry before she could become a princess.

The outdated tradition reportedly left her father fuming and he refused to pay up, but Grace was so determined to marry her prince that she eventually persuaded her father.

That said, she allegedly covered half of the cost herself from her substantial wealth amassed as a Hollywood actress.

Of course, the Monegasque royals have never addressed these reports and would be even less likely to share details of Grace's dowry and fertility test after her passing in 1982.

However, in the decades since their wedding, there has been contention over whether or not the fertility test actually happened, as well as the actual value of the dowry.

Grace of Monaco: The True Story by Jeffrey Robinson calls the fertility claims "pure invention", adding that simple fertility tests for women weren't really available in the 1950s.

Robinson also wrote that "while certain financial arrangements were made, a $2 million dowry was not involved."