Sarah Ferguson Pays Tribute To Late 'Dear Friend' Princess Diana With Poignant Birthday Post

Sarah Ferguson paid tribute to Princess Diana with a lovely birthday post on social media.

On Monday, the Duchess of York took to Instagram to honor the former Princess of Wales on what would have been her 63rd birthday.

Sharing a photo of herself with Princess Diana at Buckingham Palace to watch the Battle of Britain Anniversary Parade on September 15, 1990, she wrote:

"Happy birthday to my dear friend, Diana."

"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. Rest in peace my friend."

Viewers of the post thanked the Duchess for both her poignant message and the beautiful photo, and they wished the princess a happy birthday, as well.

Many also commented on the duo's special friendship.

Though Fergie and Princess Diana became royal sisters-in-law in their twenties, the two were close friends several years before.

Fergie told PEOPLE in 2021:

"We were best friends from when she was 14 and I was 15."

And Diana actually introduced the Duchess to her future husband, Prince Andrew.

"I said to her, 'Oh, Andrew's really good-looking.'"

"And she said, 'Duh, Fergs!'"

Later on, the two relied on each other for support.

"Diana and I both had our own mental health issues, and she and I used to talk."

"She said, 'Fergie, remember one thing: When you're at the top of the pedestal, it's so easy to fall off."

"And you're at the bottom. You just climb up.' "

She added:

"We were positioned as saint and sinner, and the most important thing was to remain robust together, and we did, no matter what anyone wrote."

Just last year, the duchess said on a Good Morning Americaappearance that she believes the two would be quite competitive as grandmothers.

"I think we'd have a Granny-Off because she would run faster in the races."

"I wonder — she'd probably be funnier. No, I think I'd be funnier."

Regardless, she thinks Di would be "very proud" of her grandchildren.

Happy Birthday, Princess Di. We certainly miss you.