Princess Margaret, who died at the age of 71, was the sister of Queen Elizabeth II, and was once engaged to Peter Townsend.
The romance began in 1947 during the royal tour of South Africa, when Peter was appointed Comptroller of the Household for the Queen Mother.
However, the romance proved controversial and the British Cabinet would not approve it which conflicted with her duties as part of the Royal Family.
Princess Margaret went on to marry Lord Snowdon, whom she divorced in 1978 after almost 20 years of marriage.
Her and her former lover Peter Townsend then went for lunch together, 30 years after their doomed romance ended.
Lady Glencoccer, a close friend of the late Princess Margaret, recounted what she said after her reunion was Peter.
She said: “Peter Townsend came to lunch with her and I said: “What was it like seeing him?”.
“She said charming, he hadn’t changed at all.”
“I looked out the window and saw him getting out of the car, he was an old man.”
“Yet in her eyes he hadn’t changed. I thought that was very touching.”
Their love story will be told on Elizabeth: Our Queen, which airs on Channel 5 tonight at 9pm.
In addition, tonight’s episode will cover the Queen’s life after her Coronation, and the world tour she took with husband Prince Philip.
It will also cover the Queen’s tough decisions as she tried to balance her family’s needs with her duties as monarch.
Last week’s episode covered Princess Margaret’s shock three words to Elizabeth as she found out she’d be ruler.
The exchange happened on 10th December 1936, which began as an ordinary day for Princess Elizabeth, who was 10 years old at the time.
She later found out her father, George VI, was to become king, leaving her first in line for the throne.
But what do you think Princess Margaret said when Elizabeth told her?