William and Kate have been accused of accidentally breaking the UK's "rule of six" after meeting Prince Edward's family at Sandringham.
The Cambridges and their children George, Charlotte and Louis, "mingled" with William's uncle Edward, his wife Sophie, and their children Lady Louise Windsor, 17, and James Viscount Severn, 13, at a Christmas attraction, reports the Daily Mail.
They were visiting Luminate, a Christmas-themed woodland walk at the Queen's Norfolk home, among other members of the public on Sunday night.
They arrived separately, and royal sources stressed there were no intentions of meeting as a group of nine. But they were photographed mixing and mingling on several occasions as they made their way along the trail.
The estate is covered by the UK's Tier Two rules, meaning only six people can meet outdoors if they are from different households or bubbles.