Karen Spencer recently moved her followers as she shared a beautiful shot of Princess Diana's final resting place to Instagram.
The Countess took to the social media site again at the weekend, where she shared another rare glimpse of an unseen corner of the family estate.
Karen, who married the late Princess' younger brother Charles in 2011, posted an image highlighting a historical detail of Althorp House that she hadn't seen before.
Sharing an image of an engraved stone which bore the legend "this house was built in 1609," she wrote: "Was in the basement (or cellars, as they like to call it here…) today turning down the heat.
"Yes, if I want to turn the heat down I have to go all the way into the bowels of the basement into the 3 different boiler rooms, one by one, and turn the boiler down. It's very old-fashioned [laughing emoji]…
"Anyway, while I was down there, I starting poking around, as I often do, and came across this amazing stone. It looks like it says 'this house was built in 1609'. Wonder where it came from. Will ask one of the old staff if they know.
"Charles said it looks half Spencer crest. I really need to have the expert on crests come back. I have lots more questions…"
As Althorp, which has been in the Spencer family for more than 500 years, was built in 1508, it can't have originated there. One of Karen's followers commented to say that the crest appeared to be the coat of arms of William Spencer, 2nd Baron Spencer of Wormleighton and his wife, Lady Penelope Wriothesley.
However their home was built before Althorp House, so its origin is still a mystery.
Earlier in the week, the Earl himself took to the social media site to share an incredible and never-before-seen family throwback. Posting a black-and-white shot of two children – an older girl and her younger brother, it was taken close to the family's Northamptonshire estate and the resemblance to Charles and his sister was clear.
The father-of-seven penned: "Just discovered – this photograph, taken by my great-grandmother Margaret Spencer in c.1900, of my grandfather Jack, and his eldest sister Delia.
"A lovely family moment, in late Victorian England. They are photographed at a spot I know well, near Althorp. I wonder what Aunt Delia has on her lap…?" His followers were quick to note the family similarity, with one writing: "That could be you and Diana. The resemblance is striking,".
Another eagle-eyed fan, meanwhile, noticed that Delia appeared to have a hat on her lap and to be holding a pair of binoculars. The Earl moved to Althorp with his family when he was 11 and Diana was 14, while their older sisters Sarah and Jane were already adults.
Now 59, Charles has no doubt been spending a lot of time thinking back to his childhood, as he prepares for next month's release of his "uncompromising" memoir about his time at boarding school.