The sweet promise Prince William made to Kate Middleton before they got married.

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Marrying into the royal family requires a lot of sacrifice.

You have to delete your Instagram and put away your open-toed shoes as you say goodbye to your old life.

But Prince William made his wife Kate Middleton’s life a whole lot easier when he made one very sweet promise before their marriage.

According to Vanity Fair‘s Katie Nicholl, speaking on the documentary Kate Middleton: Working Class to Windsor, William told Kate he wouldn’t have to leave her family behind when she married into the royal family.

Giving up your family is a very large ask, but Nicholl said by telling Kate she wouldn’t need to William was breaking tradition.

"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.

"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."

She said Prince William promised Kate that her family would always be included - and he has kept his word. It seems the Middletons and the Windsors all get on well and have been embraced as part of the wider family unit.

Kate's family have joined the Queen at Ascot and were on an important barge within the Queen's fleet at her Diamond Jubilee celebrations.

Prince Harry invited Kate's entire family to his wedding to Meghan Markle in May and when Kate's sister Pippa Middleton married James Matthews last year, Prince Harry was invited and brought Meghan along to the evening reception.

The Middletons, including Kate's parents Carole and Michael, sister Pippa and brother James, have also been seen attending church with the Windsors in the past and at Sandringham House, the Queen's private residence where the royal family traditionally spend Christmas each year.