Queen Elizabeth II and Princess Diana reportedly had a complicated relationship.

The Queen didn't approve of Camilla Parker Bowles for Prince Charles. But she didn't have a smooth sailing relationship with the late Princess of Wales either. According to Kayla Keegan of Good Housekeeping, Princess Diana and her mother-in-law had their set of differences as well. They didn't have a warm relationship like what Kate Middleton and Meghan Markle enjoy today with Her Majesty.

Prince Diana apparently felt extremely isolated and "continuously misunderstood" by the royal family. Queen Elizabeth II was reportedly sympathetic to her, but it changed over time.

When the People's Princess' marriage with Prince Charles was it its lowest, Princess Diana sought the help of the monarch. In the documentary "Diana: In Her Own Words," the princess revealed that the Queen just told her that "her marriage was loveless." The Queen was "less than sympathetic" to her.

Meanwhile, Princess Diana also challenged the monarchy. She had broken a number of royal protocols. For instance, she picked her own engagement ring. She also refused to say that she would "obey" Prince Charles during their wedding vows.

Queen Elizabeth was reportedly "stunned" when she learned about Princess Diana's biography. She didn't think that her daughter-in-law would air her "dirty linen" in such a way. But Princess Diana felt "desperate" at that time and was "at the end of her tether.'

Although the two women had a rift, Queen Elizabeth II still honor Princess Diana when she died. The monarch walked among the mourners and collected well-wishers' flowers and even gave a message on the eve of the funeral.

"I want to pay tribute to Diana myself. She was an exceptional and gifted human being. In good times and in bad, she never lost her capacity to smile and laugh, nor to inspire others with her warmth and kindness. I admired and respected her — for her energy and commitment to others, and especially for her devotion to her two boys," the Queen said.

Queen Elizabeth II also sent a letter to her closest aide, Lady Henriette Abel Smith, about Princess Diana's death. The content showed a glimpse of how the royal family felt of the princess' death.

"It was indeed dreadfully sad, and she is a huge loss to the country. But the public reaction to her death, and the service in the Abbey, seem to have united people round the world in a rather inspiring way. William and Harry have been so brave and I am very proud of them," Queen Elizabeth II wrote in the letter.

Princess Diana and Queen Elizabeth II
Pictured: Princess Diana and Queen Elizabeth II at the Braemer Highland games. Getty Images/AFP