“If it does come to pass that the Royal Foundation is split or reconfigured, I think that speaks volumes about the nature of the relationship that now operates between the four of them,” she said.
“I think that together they can make a huge difference. Obviously, Prince William is poised to be the King [of England] and Harry and Meghan are looking at a more global presence, a stronger presence in the Commonwealth, but I don’t think that means they can’t be aligned and bring that strength.
“I think the force of the four of them and the attention on the four of them being cohesive in some of these things is of such an advantage to the British public and their mission so to see them split would be really unfortunate.”
Speculation of a feud between the wives of Windsor first began earlier this year with reports claiming Meghan, Duchess of Sussex and Catherine, Duchess of Cambridge were "butting heads" in Kensington Palace.
A Palace source told New Idea at the time: "Meghan and Kate’s feud has been heightened by Meghan’s consistent thinly veiled attacks on Kate’s parenting skills – drawing up her own parenting plan ahead of the birth, which is at odds with everything Kate and William do with Prince George, Princess Charlotte and Prince Louis."
According to Ms Nicholl, the bitterness dates back to childhood at Buckingham Palace when Elizabeth Bowes-Lyon - Queen Elizabeth's mum - often favoured Prince William over Harry, making the Duke of Sussex "acutely aware of his position" in the line of succession to the throne.
Earlier this week, the Cambridges and Sussexes were all notably missing when American President Donald Trump and wife Melania Trump arrived at Buckingham Palace.
However Prince William and Kate did make an appearance at the dinner, which was attended by 16 members of the royal family including Prince Andrew, Prince Edward and Sophie, Countess of Wessex, Anne, Princess Royal, the Duke and Duchess of Gloucester as well as Prince and Princess Michael of Kent.
Mr Trumps four adult children, Ivanka, Tiffany, Eric and Donald Jr along with British Prime Minister Theresa May were also in attendance.
Prince Harry and Meghan, who is still on maternity leave with newborn royal baby Archie Harrison, stayed at home in Frogmore Cottage in Windsor.