Princess Diana's brother Earl Charles Spencer resides at Althorp House along with his wife Karen and their daughter Charlotte.
And on Monday, Karen, 51, delighted fans with the sweetest snapshot of her "gorgeous boy."
Taking to Instagram, the mother-of-three opted to share a precious image of her Labrador called Otis in honour of his 12th birthday.
She uploaded a sweet picture of her furry companion lying down in the grounds of Althorp, alongside the words: "This gorgeous boy turned 12 yesterday. Otis is definitely my dog of a lifetime."
Karen continued: "When I first arrived at Althorp his grandmother Ella and his father Karoo were living here. Ella died not too long after, but Karoo had a lovely 6 or so years before retiring to Los Angeles where he lived out his last few years in the sunshine.
"They are both buried here in the Park at Althorp with beautiful stone plaques to commemorate the spot. Hopefully Otis will, like his father and grandmother, last to 14. Fingers crossed."
Karen's post quickly caught the attention of her fans, with one commenting: "So regal. A true loving family member," while a second agreed: "Otis is a beauty. I am sure he will live a happy and loved life."
A third remarked: "Absolutely GORGEOUS @karenspencer; I'm sure you've had his portrait done but if not, this is the perfect study," and a fourth chimed in: "Such a handsome dog! Pets are very important in our lives."
It's been a busy period for Karen and Charles! The happy couple have been working hard to restore Althorp House and its sprawling 13,000-acre estate.
The Grade II listed property, which has been inherited by Princess Diana's brother Earl Charles Spencer, boasts an impressive 500-year history.
Over on Instagram, Karen spoke at length about their renovation plans, writing: "It has been over 4 years of study, working with architects and planners and our amazing team here at Althorp to imagine and carefully plan what the latest version of this wonderful house is. How do we make it work for the way we want to use it today while also being respectful of its past. I’ve spent a long time pondering this point and we are finally there!"
Alongside a photo of a wonky door, she continued: "But this door is also the perfect example of the unexpected challenges that the project presents. Just when you think you can count on a straight line, you discover you can't.
"I can't imagine how it came to be that this door is so crooked! Pipes have not been where they should be and just when you thought you knew where a beam was, it isn't… we are uncovering all this houses' secrets."