Prince George is the image of his great-grandfather, John Spencer, in an unearthed photo shared by his great-uncle, Charles Spencer.
The Earl, 60, took to his Instagram account to share the throwback black-and-white snap, which shows his father clad in military uniform in the 1950s.
Captioning the photo, he wrote: "My father, in military mode, 70 years ago. #scotsgreys #royalscotsgreys #1950s #blackandwhitephotography."
Eager royal fans quickly made the comparison between Charles' father—George's great-grandfather—and the future king. "Prince George looks a lot like him," one penned in the comments section.
A second added: "Wow, in this picture he really does [look like him]!" Meanwhile, a third wrote: "I agree!"
Other fans saw similarities between Prince Harry and his grandfather. "I can see Harry in his Grandpa," one added, alongside a red love heart emoji.
Charles lives at Althorp House, his family home where he grew up with his sisters, the late Princess Diana, Lady Jane Fellowes, and Lady Sarah McCorquodale.
Last week, Charles shared a touching tribute to his brother-in-law, Lord Robert Fellowes, who died aged 82. Lord Fellowes married Charles' sister Jane in 1978.
The couple share three children: Laura Fellowes, 44; Alexander Robert Fellowes, 41; and Eleanor Ruth Fellowes, 38.
Charles wrote: "My absolutely exceptional brother-in-law, Robert, is no longer with us. A total gentleman—in all the best meanings of that word—he was a man of humor, wisdom, and utter integrity. I'm deeply proud to have been his brother-in-law."
Robert was one of the late Queen Elizabeth II's courtiers, navigating her through her "annus horribilis" in 1992 when three of the Queen's children got divorced, and when a fire broke out at Windsor Castle.
Lord Fellowes was working for the Queen when Princess Diana, his sister-in-law, died, and he was part of the small team that advised the Queen to return to London from Balmoral.