Seen as the final step in the division of the couples’ public duties, Harry and Meghan are to break away from the Royal Foundation.
It follows reports over the past year of a rift, first between Kate and Meghan, and then between future king William and his younger brother Harry.
William and Kate will remain with the original charity, which will be renamed the Royal Foundation of the Duke and Duchess of Cambridge.
The Royal Foundation said the decision was made following the conclusion of a review into its structure.
"These changes are designed to best complement the work and responsibilities of Their Royal Highnesses as they prepare for future roles, and to better align their charitable activity with their new households," Kensington palace released in a statement.
Harry and Meghan have already split from the Cambridges’ Kensington Palace household, setting up their own at Buckingham Palace in the spring, with a separate head of communications and SussexRoyal Instagram account.
Royal aides previously said that the foursome were to remain joint patrons of the Royal Foundation.
The duke and duchess, who have recently welcomed baby son Archie Mountbatten-Windsor, also moved from London’s Kensington Palace – home to William and Kate and their children – to live at Frogmore Cottage in Windsor.
Thursday’s announcement followed William and Harry’s meeting with trustees of the Royal Foundation at Kensington Palace on Wednesday to finalise the arrangements.
William, Kate, Harry and Meghan’s joint Royal Foundation venture was intended to harness the star power of the four high-profile royals, but it lasted just 16 months after their first appearance as a foursome.
They were dubbed the Fab Four after taking to the stage together at the first – and so far only – Royal Foundation forum in London in February 2018.
The inaugural event was billed as an annual affair.
During the Q&A, they were quizzed on whether there were disagreements, with William replying “Oh yes”, while Harry said “healthy disagreements” adding he couldn’t remember if they’d all been resolved as they “come so thick and fast”.
Meghan said: “Thank goodness (there are) such differing personalities and everyone’s very communicative because that’s how you can really see bigger change.”
The Royal Foundation was set up by William and Harry in 2009 to run all their charitable campaigns and ventures, and joined by Kate when she became Duchess of Cambridge in 2011.
Meghan joined in May 2018 after becoming an HRH, with the charity’s title later officially changing to The Royal Foundation of The Duke and Duchess of Cambridge and The Duke and Duchess of Sussex.
The body set up successful charity campaigns including Heads Together, the Endeavour Fund and projects with the Invictus Games.