Britain's Kate, Duchess of Cambridge, right, with Prince Harry and his fiancee Meghan Markle attend the first annual Royal Foundation Forum in London, Wednesday Feb. 28, 2018. Under the theme 'Making a Difference Together', the event will showcase the programmes run or initiated by The Royal Foundation. (Chris Jackson/Pool via AP)

Prince Harry has admitted working with his family has its "challenges", and joked disagreements come "thick and fast".

The 33-year-old royal, his brother Prince William, 35, and Duchess Catherine, 36, welcomed Harry's wife-to-be Meghan Markle into The Royal Foundation - the main vehicle to pursue the young royals' charitable interests - on Wednesday, and the prince joked there are "challenges" working as a foursome. 

When asked at an event at the City of London to highlight the Foundation's work if there are family disagreements, William quipped: "Oh, yes."

Harry said: "They come so thick and fast. Working as family does have its challenges, of course it does. But we're stuck together for the rest of our lives."

The flame-haired prince also admitted he and Meghan are "pretty tied up" planning their upcoming wedding, which will take place on May 19, 2018, but will try to do as much work as possible beforehand. 

He said: "We're pretty tied up with planning a wedding, but we want to make as much of a difference as we can."

While Harry joked about being "stuck" with his family, Catherine - who has two kids, Prince George, four, and Princess Charlotte, two, with William, as well as another on the way - admitted the quartet are in an "unusual position" in that their roles are forever. 

She added: "Since our roles are lifetime roles, our commitment to the work we do through The Foundation is genuinely long-term.

"The work we do can, and should, have a long-lasting resonance. For this reason, we are able to support causes which we're passionate about for decades into the future. Rather than just for a few months or years.

"Like the queen, the Duke of Edinburgh, and the Prince of Wales, we feel strongly that we have to take a long-term view that is measured in generations. 

"This perspective allows us to take time to really learn about and understand the issues, and then assemble the right group of experts and partners to form coalitions to create sustainable solutions.

"It is an unusual and privileged position to be in, but I do think this long-term view will ultimately help us make a difference in the areas that we care so passionately about."