Charles seemed touched by the sentiment as he captioned the image, “Received at @AlthorpHouse today - amazing, and touching.”
The Earl has had issues with the royal family since his speech at Princess Diana's funeral in 1997, where he claimed his sister was the “the most hunted person of the modern age”.
According to Express UK, the Queen was reportedly “disappointed” and “saddened” by the speech.
In addition to this statement, Charles made several thinly veiled comments about the British royal family during his speech.
Charles said his sister “needed no royal title to continue to generate her particular brand of magic” and that "it is a tribute to her level-headedness and strength that despite the most bizarre-like life imaginable after her childhood, she remained intact, true to herself.”
Meanwhile, Diana’s son Prince Harry marked his mother’s birthday by sharing a poignant anti-racism video.
In the video posted for the 2020 Diana Awards, Harry said: "My wife [Meghan Markle] said recently that our generation and the ones before us haven't done enough to right the wrongs of the past," in reference to the Black Lives Matter movement which has been front and centre in the wake of the George Floyd protests.
"I too am sorry - sorry that we haven't got the world to a place you deserve it to be."
The Duke continued: "Institutional racism has no place in our societies, yet it is still endemic," he continued. "Unconscious bias must be acknowledged without blame to create a better world for all of you."