In her very first interview after her engagement to Prince Harry, Meghan, Duchess of Sussex, gushed that her sister-in-law Kate had been "wonderful" by welcoming her into the royal family from day one.
But in a matter of months, tensions between the duchesses have reached boiling point.
Now, after weeks of speculation about what came between dutiful Kate and Meghan, who has been nicknamed "Duchess Difficult" and "Hurricane Meghan", palace insiders have finally spoken out with the truth, revealing the newest royal recruit has snubbed the Duchess of Cambridge, 36, in what is being labelled as the ultimate act of betrayal.
After weeks of conjecture surrounding a feud between the women, our palace insider reveals the tension is all due to Meghan becoming green with envy over Harry's close bond with Kate.
The Duchess of Cambridge has always had a close friendship with William's younger sibling. As well as offering him romantic advice and teaching him how to cook, she apparently joins her 34-year-old brother-in-law to watch TV show Game Of Thrones.
"Kate and Harry get along brilliantly. They're always laughing when they're together and people think Meghan is incredibly jealous of their bond," a royal aide explains.
It drives Meghan "berserk" that Kate can do no wrong in the eyes of the public, the monarchy – and Harry. And now, according to insiders, she is hellbent on tearing them apart. It's a real stab in the back for Kate, who's gone above and beyond to welcome Meghan into the royal fold.
"When Harry told William and Kate he'd finally found The One, they couldn't wait to meet her," a palace aide tells Woman's Day.
"Kate knows how daunting it is to become a royal and to have to learn about everything that comes with the role. She bent over backwards to help Meghan settle in and give her guidance and training. Now, it's as if Meghan is throwing that back in her face."
The duchesses appeared to be future BFFs during their first joint interview in February 2018, and even attended Wimbledon together in July.
The fast friendship gave hope to royal fans that Meghan, Harry, Kate and William would become a tight-knit awesome foursome, but now those hopes are dwindling fast! Many say Meghan's envy over Kate has caused an onslaught of diva-ish demands and behaviour on her part.
In recent weeks, whispers from the palace have claimed Kate was left in tears at a bridesmaid fitting for Princess Charlotte ahead of Meghan and Harry's wedding. And on another occasion, Kate is said to have reprimanded Meghan, 37, for telling off a member of her staff.
It quickly became apparent Meghan was less than impressed at taking direction from Kate, no matter how well-meaning her intentions.
"Meghan is not afraid of bending the rules and although Kate has been on hand to give her advice at every turn, Meghan has made it clear that she would rather figure things out for herself. It's been a slap in the face for Kate," reveals the insider.
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"She prefers to just focus on herself and Harry as a couple, and now their new baby. That's why Meghan is so keen to move out of Kensington Palace and have some space away from William and Kate."
"Duchess Difficult" is also understood to be so demanding that several members of staff – including the duchess' personal secretary who has worked with the royals for 17 years – have quit.
The former actress' jealous streak has not only caused havoc at the palace, Harry's relationship with his 36-year-old brother has become frayed as a result. "William and Harry were close but this has caused tension," says our insider.
Now Woman's Day has learned the Queen is up in arms about the discontent in the palace.
Last week Kate was spotted driving through the gates of Buckingham Palace to meet the 92-year-old monarch. The Queen is leaning on Kate to uphold the royal family's reputation and it's believed she called the mum-of-three to the palace for crisis talks.
"The last thing Her Majesty wants is for there to be negative rumblings surrounding the royals. She's begging Kate to do what she can to fix the debacle," adds the insider. "The duchess is willing to put her differences with Meghan aside for the sake of the royal family, but she's heartbroken.
"Kate was at first thrilled to have a sister-in-law she could turn to but Meghan has shunned her, leaving Kate feeling incredibly betrayed."