Princess Diana could have immediately left Prince Charles upon discovering his infidelity, but she did not. 

Prince Charles' unfaithfulness towards Princess Diana was one of the most controversial issues that the royal family had ever faced.

Even before she discovered her husband's infidelity, the Princess of Wales already suffered, as she struggled with her mental issues alone. for his part, Prince Charles made everything worse.

If Princess Diana did not overlook all the problems she went through with Prince Charles, she could have ended her relationship with him immediately. However, a royal expert revealed what took her so long to divorce the Prince of Wales.

In the 1992 book "Diana: Her True Story," royal author Andrew Morton revealed that Princess Diana "delayed" the legal separation out of her respect for Queen Elizabeth II.

"While Diana finds the monarchy as presently organised as a crumbling institution she has a deep respect for the manner in which the queen has conducted herself for the last forty years," Morton wrote. "Indeed, much as she would like to leave her husband, Diana has emphasised to her: 'I will never let you down.'"

Princess Diana had to endure more years being with Prince Charles for Queen Elizabeth II and their two sons, Prince William and Prince Charles.

Meanwhile, although she wanted to end her marriage as soon as possible, the documentary "Diana: In Her Own Words" unveiled how the Princess of Wales recalled the time when she tried to seek advice from the Queen about her relationship with the heir to the throne.

In 1986, the late royal princess reportedly went to Queen Elizabeth II, sobbing and asking for assistance since she felt like her life with Prince Charles was "loveless."

"I went to the top lady and said: 'I don't know what I should do," Princess Diana narrated. "She said: 'I don't know what you should do.' And that was it. That was 'help.'"

Despite that incident, Princess Diana famously showed her respect to the Queen in public when they attended an event on a hot day.

Despite the humid environment, the Princess of Wales refused to fan herself since Queen Elizabeth II would not be using one.

"[Princess Diana said] 'My mother-in-law is going to be standing there with her handbag, gloves, stockings, and shoes.' It was a sentiment expressed in admiring tones for the Sovereign's complete self-control in every circumstance, however trying," Morton mentioned in the same book.

Princess Diana A "Great Loss" To The Monarchy

After Princess Diana died in a tragic car incident in 1997, Queen Elizabeth II expressed the same amount of respect to her through a heartfelt address to the nation.

"I want to pay tribute to Diana myself," the Queen began. "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."

Her Majesty added that she admired and respected her not only as the people's princess, but also as a mother to Princes William and Harry.

Aside from the address, the monarch reportedly wrote a letter six days after the incident wherein she called Princess Diana as "a great loss" to the monarchy and the country.

READ MORE: Royal Outrage: Queen Elizabeth II DISRESPECTED In Netflix Series' The Crown'