Princess Diana was the 'first person to rattle the cage of the monarchy'

The Queen's biographer has revealed what it was about Diana that rattled the monarchy. Photo / Getty Images

Princess Diana was the "first person to rattle the cage of the monarchy", claims the Queen's biographer.

The late Princess of Wales - who died in August 1997 in a car crash in Paris aged 36 alongside her boyfriend Dodi Al-Fayed - was the only person "in living memory" to question how the institution runs and operates.

However, new claims suggest she didn't do it "intentionally" but rather accidentally with her AIDS and landmine activism and the way she captured the national imagination.

The Queen's biographer Ingrid Seward told People magazine: "Diana was the first person to rattle the cage of the monarchy within living memory.

"I don't think Diana went out intentionally to change the family. She did it because that was the way she was."

Princess Diana and Prince Charles with Prince William. Photo / Ross White

Her death - which sparked a wave of grief across the world - caused the Queen to be widely condemned for her lack of public mourning but has used the lessons learned from the backlash and learnt from her "legacy".

Seward said: "The Queen can now see Diana's legacy is a huge force for good."

Princess Diana - who caught flack from the royal family about how she courted the press - was involved in an unhappy marriage with Prince Charles, who married her in 1981 when she was 20 and he was 32, after he was still involved with Camilla Parker-Bowles, who he eventually married in 2005.

Andrew Morton, who collaborated with Diana secretly on his 1992 book Diana: Her True Story - In Her Own Words, believes that the 72-year-old future King "will be remembered" for their union coming to a close in 1992 after they had two children together; Prince William, now 40, and Prince Harry, 37.

He said: "His tragedy is whatever he does, whatever he says, however he behaves, he will be remembered for one thing: the fact that his fairy-tale marriage ended. Just as Henry VIII is remembered for his six wives, Prince Charles is remembered for his first wife.

"It will always haunt him. His life has been defined by his marriage."