According to inside sources, Kate Middleton has been working diligently to keep Meghan Markle, her estranged sister-in-law, from attending King Charles III's coronation. RadarOnline.com has learned that Kate is now trying to ensure Prince Harry's wife is permanently excluded from the UK.

A palace courtier disclosed to RadarOnline.com that "it's becoming increasingly apparent Kate was the mastermind behind Harry's solo appearance at the coronation," and had plans to make sure Meghan would have had "a rotten time" if she had chosen to attend.

Another insider revealed that Kate informed her father-in-law, Charles, that she was unwilling to reconcile with the Suits actress, whom she blames for irreparably damaging Harry's relationship with the royal family.

Harry, 38, and Meghan, 41, left royal duties behind to pursue fame and fortune in Hollywood two years after their extravagant 2018 wedding. Harry criticized his relatives in revealing interviews and his contentious memoir, Spare, which portrayed his father as "cold" and referred to his stepmother, Queen Camilla, as a "villain."

As reported by RadarOnline.com, Kate and Meghan have never been on good terms, with tensions arising early on in Meghan's relationship with Harry. In the Netflix documentary Harry & Meghan, Markle recounted her first meeting with Kate and Prince William, which highlighted cultural differences and was an introduction to royal etiquette for her.

Sources claim that Kate attempted to help Meghan acclimate to the royal family, but Meghan was unreceptive to her advice. "William's wife has not forgiven Meghan for her American-style mean girl behavior," an insider shared.

Kate, now the Princess of Wales, reportedly sees her sister-in-law as a "toxic thorn" in the monarchy's side and is determined to remove it. "Kate fully supports her husband's decision to spurn his kid brother if that's what it takes to bring Harry to heel. She sees the self-absorbed Sussexes as a threat to the monarchy — and as a future Queen of England her opinion carries significant weight," the source said.

The insider claimed that keeping Meghan in California for Charles' coronation was a victory for Kate, but she won't stop there. "She played her cards right and won," the source said. "You can bet she'll make sure Meghan stays as far away as possible in the future — and maybe be gone for good."