There’s somethng undeniably captivating about royal romances. The union of Prince Charles and Princess Diana once seemed like a real-life fairy tale, but as the world came to learn, their marriage was far from perfect.

Still, the couple had two sons—Prince William and Prince Harry—who became second and third in line to the British throne at the time. Though their marriage ended in divorce shortly before Diana’s tragic death in 1997, countless photographs of the couple remain. As one of the most iconic royal pairs in modern history, they were endlessly documented.

But something curious about those photos has surfaced in recent years. In March 2017, sociologist Philip N. Cohen pointed out a visual inconsistency: in many official portraits, Diana appears noticeably shorter than Charles. Yet in reality, they were roughly the same height.

Cohen highlighted this with a series of tweets showing various examples, drawing attention to what many had accepted without question. Candid shots and video footage confirm the two were nearly eye-to-eye, raising the question—why did Charles appear so much taller in formal photos?

One clue may lie in Diana’s choice of footwear. It seems she frequently wore flat shoes when photographed with Charles, likely to emphasize a more traditional height difference. Now that the detail’s been brought to light, it’s hard to ignore.

Diana, born into the aristocratic Spencer family, had longstanding ties to the Crown. Her connection to royalty grew official in 1981 when she became engaged to Prince Charles and later married him in a spectacular ceremony, earning the title Princess of Wales.