While many people believe Princess Diana and Sarah "Fergie" Ferguson fell out before Diana's tragic death, The Duchess of York has shut down these rumours once and for all.
The Duchess has revealed the pair's unshakeable bond, which she said saw them through to the very end.
"We promised each other we would always be together – there was never any daylight between us," the 61-year-old told People magazine.
"But everybody wanted that because we were so strong together. People want to break something so strong."
The duo first met when they were teens before they both went on the marry Queen Elizabeth's sons.
"We were best friends from when she was 14 and I was 15," she told People, sharing that her nickname for Diana was always "Duch".
"She taught me so much of public life," Ferguson said. "She was so brave. We used to have the most incredible time together."
Ferguson married Prince Andrew in 1986 before the pair divorced in 1996. The pair share two daughters, Princess Beatrice and Princess Eugenie, who both recently wed.
"[Diana] adored my girls," Ferguson shared. "She adored [her] boys. This would be her haven. Her heaven.
"She would be very proud of her sons and their wives," she said. "And she would be just like me, obsessed with her grandchildren. Because that's what she loved … If she were sitting with me right now, I know she would say, 'I am so proud of both of my boys and the wonderful wives they have chosen.' Because each has got her own voice."
Diana was married to Prince Charles from 1981 until 1996 and died in 1997 in a Paris car crash. The Princess was aged 36.
On July 1, Diana's 60th birthday, William and Harry reunited to unveil a statue of their late mother in the Sunken Garden at London's Kensington Palace.
Diana is said to have found solace in the garden.
The statue was commissioned by the brothers in 2017 and was meant to showcase Diana's confidence she gained from her humanitarian work.
"Today, on what would have been our mother's 60th birthday, we remember her love, strength and character – qualities that made her a force for good around the world, changing countless lives for the better," William and Harry said in a statement.
"Every day, we wish she were still with us, and our hope is that this statue will be seen forever as a symbol of her life and her legacy."