The Princess of Wales' revelations sent shockwaves around the world.
In 1995, BBC's Martin Bashir spoke to Princess Diana in a solo interview, where she revealed that she knew about her husband's extramarital affair, as reported by Pop Sugar.
When Bashir asked her if she thought Camilla Parker-Bowles was a factor in the breakdown of her marriage with Prince Charles, the People's Princess infamously said: "There were three of us in this marriage, so it was a bit crowded."
In the interview, Diana also shared that she informed Prince William, then 13, about his father's relationship with Camilla.
The Princess of Wales said that she told William, "If you find someone you love in life, you must hang onto it and look after it. And if you are lucky enough to find someone who loves you, then you must protect it."
Diana went on to say that she didn't want to end her marriage with Charles. But she was left with no choice and that they needed to clarify their situation.
"I await my husband's decision of which way we are all going to go," she explained.
Charles and Diana tied the knots in 1981. Their wedding was considered as one of the biggest TV events in history.
The royal marriage soon fell apart. During that time, Charles was obviously in love with Camilla, whom he had a brief relationship with in the 1970s.
Though she faced many problems, Diana always appeared in public with a beautiful smile.
The mother-of-two reportedly fought her husband. She then suffered from anxiety, bulimia, depression, and self-harm.
As the result of a loveless marriage, Diana and Charles eventually separated in 1992 and divorced in 1996.
Diana was killed in a car crash in a Paris tunnel on August 31, 1997. She was 36 years old at the time.
As Princess of Wales, Diana was celebrated for her charity work around the world. She also raised awareness and advocated ways to help people with HIV/AIDS, cancer, and mental illness.