Prince William made this endearing pact with Kate Middleton before tying the knot

Prince William and Kate Middleton had a whirlwind romance that lasted for almost a decade.

The Duke of Cambridge was unsure at first if he should marry Kate. However, he made a promise to her before tying the knot, that he is keeping even after years of marriage.

In the Amazon Prime documentary Kate Middleton: Working Class to Windsor, royal correspondent Katie Nicholl revealed William ensure Kate she will have plenty of time to spend with her own family, the Middletons.

"Once you married into the royal family, you became a Windsor and that was that. Well, it was different when Kate and William got married," Nicholl explained, according to The Sun.

"When William asked Kate to marry him, he made it very clear that she wouldn't have to leave her family behind her once she married into his family. He promised her that they'd always stay a part of the family and they have done.

"Whether it's joining the Queen at Ascot or being on an important barge within the Queen's fleet at the Diamond Jubilee celebrations, they've been there," she added.