Queen Elizabeth has a complicated relationship with her daughter-in-law, Camilla, who was first married to Andrew Parker Bowles before she became Prince Charles' second wife. Her Majesty was quite fond of her when she was still with her first husband.
But the Queen grew to dislike Camilla when she started seeing the Prince of Wales, Prince Charles, who was still married to Princess Diana, the Princess of Wales. Royal biographer Penny Junor said that it was not a personal dislike. However, as the monarch, Her Majesty saw Camilla as the person responsible for the Wales union's breakdown.
Junor said that Queen Elizabeth wanted Camilla gone from Prince Charles' life ever since she found out about the affair. Her stance didn't change when Diana died in 1997 but her son apparently "made it clear" he needed Camilla in his life, who had divorced from Andrew in 1995.
Queen Elizabeth decided to ban Camilla from Buckingham Palace's events to show her disapproval. It was a difficult and uncomfortable decision because Camilla's first husband was the Queen Mother's godchild. The Parker Bowles had been part of the Palace's social scenes before.
According to Daily Mail, the threat of Camilla to the monarchy was different. The Queen's one fear was that if she died and Charles becomes the King, while still unmarried, then Camilla would still be on the sidelines as his mistress. The thought of having a consort as a mistress could ruin the British monarchy.
But while Charles could technically remarry right after Diana's death, Queen Elizabeth didn't want to push it as there could be more hostility towards the royal family. Getting rid of Camilla's tag as the "mistress" needed to be done at the right timing.
Junor also revealed that Queen Elizabeth only got to know Camilla better during a party for the Greek King Constantine in 2000. This became the turning point for the two women as signs indicated a thawing relationship.
By 2003, Camilla moved into Clarence House, Prince Charles' official house. Two years later, after 35 years of knowing each other, the couple announced their engagement. For the royal courtiers and senior staff members, marriage was the only way Charles and Camilla could win back everyone's favor.
Queen Elizabeth did not attend the civil wedding, but she was present at the reception and was in the family photos with Prince William and Harry. By 2016, Queen Elizabeth included her daughter-in-law to the Privy Council, her senior advisors, confirming that Her Majesty has finally accepted the Duchess of Cornwall.
In 2017, Camilla said an interview that the years her affair with Prince Charles landed on the front pages was a "deeply unpleasant time" and she doesn't wish this kind of scrutiny from her worst enemy.