Princess Diana and Queen Elizabeth II through the years. Terry Fincher/Princess Diana Archive/Getty Images, Dirick Halstead/Getty Images

Princess Diana knew Queen Elizabeth long before she got engaged to Prince Charles, as she had grown up in royal circles. Her father was an equerry to the Queen, according to The Independent.

Lady Diana Spencer and Prince Charles pose with Queen Elizabeth at Buckingham Palace, London, in March 1981, the day that their wedding was sanctioned by the Privy Council. Bettmann/Getty Images
Source: The Independent

They had a polite but formal relationship, according to Diana’s biographer Andrew Morton. This is evident in an image of Diana and the Queen before the wedding, where they shared a kiss on the cheek.

Lady Diana Spencer gives Queen Elizabeth II a kiss on the cheek before watching Prince Charles play polo on July 1, 1981. Dirck Halstead/Getty Images
Source: Tatler

Diana curtsied to the monarch publicly for the first time at her royal wedding at Westminster Abbey on July 29, 1981.

Princess Diana curtsied to Queen Elizabeth II before her wedding to Prince Charles on July 29, 1981. Tim Graham Photo Library via Getty Images

Queen Elizabeth looked on as Charles and Diana shared their first kiss on the palace balcony, marking the first time a royal couple did so.

Princess Diana and Prince Charles kiss on the balcony of Buckingham Palace after their wedding on July 29, 1981. Tim Graham Photo Library via Getty Images

Through the years, Diana accompanied the monarch to official engagements. In this photo, taken in November 1982, they traveled together to the State Opening of Parliament.

The Princess of Wales and the Queen attend the Opening of Parliament in London, November 1982. Terry Fincher/Princess Diana Archive/Getty Images

The royal ladies knew how to share a laugh together. Here they are with other members of the royal family as they celebrated the Queen Mother’s 87th birthday in 1987.

The royal family gather for The Queen Mother’s 87th birthday on August 4, 1987. Princess Diana Archive/Getty Images

Diana and the Queen were cordial, even when the princess’ marriage broke down. Here, they are pictured at Trooping the Colour in 1992, the same year of the Wales’ separation.

The royal family on the Buckingham Palace balcony for Trooping the Colour 1992. Jayne Fincher/Princess Diana Archive/Getty Images
Source: The Guardian

They appeared in public together long after Diana and Charles’ public split. In this photo, they wore matching lilac outfits as they attended a royal engagement in 1994.

Princess Diana and Queen Elizabeth at the Canada Memorial Foundation Monument in Green Park, London, in June 1994. Tim Graham Picture Library/Getty Images

Diana died in a car accident in Paris on August 31, 1997. The monarch paid tribute to the princess with a speech, saying she “was an exceptional and gifted human being.”

Queen Elizabeth delivers a speech in tribute to Princess Diana on September 5, 1997. Ap Archive, YouTube

“She was an exceptional and gifted human being. In good times and bad, she never lost her capacity to smile and laugh, nor to inspire others with her warmth and kindness,” the Queen said in a televised speech at Buckingham Palace on September 5, 1997.

“I admired and respected her — for her energy and commitment to others, and especially for her devotion to her two boys. This week at Balmoral, we have all been trying to help William and Harry come to terms with the devastating loss that they and the rest of us have suffered,” she added.