Charles Spencer often shares fascinating photographs of the sprawling Althorp estate in Northampton where he lives and the stunning surrounding areas.
However, the Earl occasionally posts snaps of his family and ancestors, much to the delight of his loyal 240k followers.
The brother of the late Princess Diana, 60, took to his Instagram over the weekend to share an old photograph of his grandfather at the historic residence over a century ago – and fans were stunned to see the resemblance to Charles' nephew, Prince William, and even William's eldest child, Prince George.
Charles captioned the sepia-toned snap with some details: "My grandfather Jack Spencer on his horse, 'Marbury', in front of @althorphouse in January 1911."
While many were thrilled that Charles had shared the fascinating relic, others were quick to point out the similarities between William and his great-grandfather.
One fan summed it up: "Prince William looks like him!" and another agreed: "Do you think William has a look of him?" A third echoed this but also noted: "I see some Prince George in him."
While a fourth wrote simply: "The Spencer men are very handsome, the women beautiful. Lovely family! Thank you, Sir, for sharing another family photo."
This is not the first time that Charles's family photographs have sparked such a reaction from royal fans.
Earlier in the summer, the Earl shared a snap of another relative – his grandfather, John – whom fans also thought had a strong resemblance to the Prince and Princess of Wales's eldest son.
"Prince George looks a lot like him," one penned in the comments section, pointing out the "strong" Spencer genes.
Charles Spencer and history of Althorp
Meanwhile, Charles has overseen the Grade I listed property ever since the death of his father John in 1992. It's been in the Spencer family for over 500 years and is set on 13,000 acres of land.
He married his third wife, Karen, Countess Spencer, 52, in 2011 after the couple were initially set up on a blind date in Los Angeles the previous year, with the Earl proposing at Althorp.
They share a daughter Charlotte Diana, who was born in 2012, but announced the sad news of their divorce earlier this year. After announcing their separation, Karen has continued to reside at the Northampton home but explained more recently that she would be relocating.
"I'm looking forward to reconnecting with everyone on social media soon," she said last week. "I'll be posting more regularly again starting in September.
"I'm currently still at Althorp, and as we move into the fall, I look forward to closing this chapter out with you all and launching the next. I will be sharing an update on my projects and reflecting on all the wonderful things I have learned during my time here on this beautiful Estate."