Queen Elizabeth II and Prince Philip have been married since 1947. That means that they’ve spent more than 70 years married to one another. During that time, they’ve raised a family and set records as the longest-reigning British monarch and the longest-serving consort. But they’ve also cultivated a loving relationship that royal family fans around the world admire.

But people also have questions about how Queen Elizabeth II and Prince Philip appear in photos together. For instance, why does Prince Philip always walk behind the queen? Here’s what you need to know.

Why does Prince Philip walk behind Queen Elizabeth II?

Prince Philip typically walks behind Queen Elizabeth II. There’s a very specific reason why: the Orders of Precedence. As Reader’s Digest reports, when the royal family is part of a procession, they enter and are seated in the order of precedence. That’s essentially the same order as the line of succession to the throne. The order is Queen Elizabeth II, the Duke of Edinburgh, the Prince of Wales and the Duchess of Cornwall, the Duke and Duchess of Cambridge, and so on.

Because she’s at the top of the royal family’s hierarchy, Queen Elizabeth II walks at the front (particularly for formal occasions and state dinners). Prince Philip, the Duke of Edinburgh, walks behind her out of respect for the orders of precedence. After all, even though Prince Philip is the husband of the queen, he isn’t king, and in fact, wasn’t “Prince Philip” until Elizabeth became queen.

As users on Quora point out, the Prince of Wales, as the heir apparent, should technically rank higher than Philip. But the queen can update the orders of precedence. The queen issued a letters patent to accord the Duke a position higher than all other male members of the royal family. Similarly, Camilla, Duchess of Cornwall, ranks behind the queen, Princess Anne, and Princess Alexandra, even though she should rank second-highest.

The custom may have caused tension early in their marriage

The Netflix series The Crown has shed light on many royal customs, “including some that reportedly caused tension early in Elizabeth’s marriage to Prince Philip,” The New York Times reports. Matt Smith, who plays the young Prince Philip in the series, told the Times that researching the role of Prince Philip had made him aware of what “an interesting, dramatic and painful life” the Duke of Edinburgh has led.

“He has a great wit, was a wonderful naval man, a wonderful family man,” Smith explained. After his young wife becomes queen, he added, “He is going to walk two steps behind her, wanting to feel the head of the family. It’s an interesting conflict to explore.”

Claire Foy, who plays the young Queen Elizabeth II in the series, also said, “She wasn’t supposed to be queen, and the family suddenly had that thrust upon them.” Foy added, “And then her marriage with Philip had to change. I think they would have liked a conventional life where the man goes out to work, and the woman stays home.”

The couple’s body language hasn’t changed much over the years

Queen Elizabeth II and Prince Philip may look very different than they did when they first got married. But according to Good Housekeeping, body language experts say that the couple’s body language hasn’t changed very much over the years. They don’t engage in much PDA, and they keep their body language formal during public appearances. But despite that, “you clearly see Prince Phillip’s love and adoration for his Queen,” Good Housekeeping notes.

Even when he walks behind his wife, the Duke of Edinburgh stays close to her. He often leans toward her, indicating that he’s focused on her, even when she stands on her own to signal her independence. They also don’t hold hands in the same way that Prince Harry and Meghan Markle, for instance, might. Queen Elizabeth II usually reaches for Philip’s hand or arm for assistance, but he’s always ready and waiting for her.

Read more: Everything ‘The Crown’ Got Wrong and Right About Prince Philip

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