Was it a mistake? Prince William and Kate Middleton snubbed Prince Harry’s royal title in a post for his 36th birthday on Tuesday, September 15. The Duke and Duchess of Cambridge took to their Instagram to wish him a happy birthday—but they may have left out some crucial words.

The post, which showed William, Kate and Harry running in a race as Harry was a few sprints ahead of his brother and sister-in-law, was captioned with: “Wishing a very happy birthday to Prince Harry today! ” As sweet as the post was, some fans noticed that William and Kate didn’t call Harry by his royal title, the Duke of Sussex, unlike other royal family members.

Unlike William and Kate, Harry’s grandparents, Queen Elizabeth and Prince Philip, did use his royal title in their Instagram post for his birthday. The Queen shared a photo of her and her grandson from an event as Harry smiled at his grandmother. Queen Elizabeth and Prince Philip captioned the post, “  Wishing The Duke of Sussex a very happy birthday! . The Queen and The Duke during a Queen’s Young Leaders reception at Buckingham Palace in 2017.”

Likewise, Harry’s father, Prince Charles, and Charles’ wife, Camila, the Duchess of Cornwall, also used Harry’s “Duke of Sussex” title in their birthday posts. For Harry’s birthday, Charles and Camila shared two Instagram photos of the Duke of Sussex. One was a solo picture of Harry while the other was a photo of Harry and his father at the Invictus Games. “Wishing a very happy birthday to The Duke of Sussex today! ,” the caption read.

Source: Instagram

Source: Instagram

Source: Instagram

So what was William and Kate’s deal? Though it could’ve been an oversight, some fans think that the Duke and Duchess of Cambridge’s post was shade at Harry after he and his wife, Meghan Markle, announced their decision to step down as senior members of the royal family in January. The couple, who have since moved to Santa Barbara, California, completed their last day as senior royal members on April 1.

“Thank you to this community – for the support, the inspiration and the shared commitment to the good in the world. We look forward to reconnecting with you soon. You’ve been great! Until then, please take good care of yourselves, and of one another. Harry and Meghan,” Harry and Meghan wrote on their Instagram at the time.

In a statement on their website at the time, Harry and Meghan announced that they will no longer use the words “royal” or “Sussex royal” for anything related to their brand. Their announcement also stated that they cease the use their “HRH” titles (His/Her Royal Highness) as they are no longer senior members of the royal family. Harry and Meghan, however, did confirm that they will still keep their Duke and Duchess of Sussex titles, which is why royal family members (with their exception of Will and Kate) continue to refer to them as the Duke and Duchess in Instagram posts and other official statements.