Sarah Ferguson Honors 'Dear Friend' Princess Diana on Late Royal's 63rd Birthday: 'What a Legacy You Left Behind'

Sarah Ferguson took to social media to pay homage to her late pal Princess Diana, who would have turned 63 on Monday, July 1.

“Happy birthday to my dear friend, Diana," Ferguson wrote in an Instagram post. "You were a pillar of light and love. And what a legacy you have left behind. I will forever remember our laughter and the kindred, kind spirit I found in you."

"I am sure you are watching over us always," she added. "Rest in peace, my friend.”

Diana and Ferguson developed a close bond — something the Duchess of York reflects on often.

“We promised each other we would always be together – there was never any daylight between us,” the famous redhead said in an interview. “But everybody wanted that because we were so strong together. People want to break something so strong.”

Although Prince William and Prince Harry protect their mother's legacy, they didn't reunite this year amid their yearslong feud. OK! previously reported an insider claimed Diana's fatal car accident in Paris traumatized the Duke of Sussex.

“Harry was scarred by what his mother went through, and when he saw the same thing happening to Meghan , he knew he must act,” the source explained. “He’s certain his mother would have approved of him leaving the royal family. Diana had tried to do the same, and he thinks she would be proud of him and his new life .”

According to the confidant, this time of year is emotionally taxing for Harry.

"Diana’s birthday is painful for Harry and William both,” said the source. “For Harry, he thinks about what could have been, and William is reminded of being without her from such a young age. The loss of their mother cuts deep.”

Aside from celebrating Diana, an anonymous insider hinted at Kate Middleton 's cancer battle being a potential catalyst for a reconciliation.

“Both Harry and Meghan have been following Kate’s recovery with huge interest, but, sadly, it’s had to be more from afar because their lines of communication with the palace and the Waleses, in particular, are very limited, to say the least,” a source said. “They have had enough information to know that people are excited about the idea of a comeback for Kate , and they’re both relieved and happy to hear that she’s on the mend and may soon be well enough to return to her duties.”

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When Kate announced she has cancer, the Sussexes released a statement supporting the Princess of Wales.

"They’ve jointly reached out to send well-wishes, but they’re still not really in a place with Kate to warrant much of a response,” the source admitted. However, they noted that the Wales' silence “hasn’t stopped them from trying to connect.”

“When Kate gets back into action, their hope is that it might take some of the heat off them and possibly trigger a truce with her and William , and with the King , too,” the insider said of the American-based royals, who are now based in California.

Ferguson spoke to People .