Their public appearances together were few and far, which is no surprise given the Princess of Wales and Meghan Markle never really hit it off.
The pair were only seen in public together a handful of times before Meghan and husband Prince Harry - who dished on the tensions between the two caused by comments over hormones and a badly fitted bridesmaid dress - decided to quit the UK to carve out a new life with their children in America.
However, one of their last joint outings took everybody by surprise - and it came when the foursome did a walkabout just days after the late Queen's death to look at the floral tributes and greet wellwishers at Windsor Castle. Many hoped this outing could have paved the way for reconciliation. But instead, it has been claimed that Kate found carrying out the appearance one of the hardest things she's ever had to do.
Kate and Meghan appeared not to talk to each other during the Windsor walkabout (PA)And during this outing, body language expert Judi James noted one "storming gesture" by Kate that suggested she was in no mood to make up with sister-in-law Meghan - despite the seemingly united front. She told the Mirror: "The first sight of the two couples that day was when the car they were all travelling in pulled up outside the gates of Windsor Castle.
"As the car drove up it was clear the two couples had shared the ride. The right-hand doors opened and Harry got out, followed by William. Despite their differences, the brothers kept close together and even stood together to make their greetings.
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"Kate got out the other side with Meghan behind her. Kate's first gesture of intent came as she stormed around the car to join the brothers without as much as a backward glance at Meghan. She was clearly going to make no attempt to play at small talk or unity.
"Meghan went to follow at a distance but held back as though unsure whether to join the others or not. While Kate ignored the Sussexes it was William who noticed Meghan and extended an arm to invite her to join them. Meghan hung back in the group and Harry squeezed round behind his brother to get to his wife, who was standing nervously tossing her hair."
Harry didn't spare Kate any criticism and revealed private details about a falling out between her and Meghan in his memoir Spare. He also described how Kate allegedly 'grimaced' when Meghan borrowed her lipgloss and how the women had a disagreement after the Duchess of Sussex said William's wife had "baby brain" after Prince Louis was born.
Royal expert Jennie Bond says Kate was hurt and insulted by the attacks by Harry and Meghan - and it's unlikely their feud will be fixed any time soon. Speaking to OK!, she said: "When you come from a happy, united family – as Catherine does – it's incredibly hard to understand how people can become estranged.
"I think she believed the rift could be fixed and, after Prince Philip’s funeral, we saw her talking with Harry and obviously encouraging William to do the same. But we now know that it didn’t work. In fact, William and Harry had a blazing row right after the funeral. There comes a point when you just have to accept that happy families are not a game that everyone can play.
"Catherine has been hurt and insulted by things that Harry and Meghan have said, but she and William are a very strong team, and I suspect that, together, they’ve come to the conclusion that the rift with Harry cannot be fixed in the foreseeable future. They’ve closed their minds to that possibility and decided to get on with their lives."