Yesterday was Father's Day, and—as is tradition—members of the Royal Family took to social media to celebrate. There was more than one reason, too. June 21 also marks Prince William's birthday, so he spent the day opening double the amount of presents, we can presume.

To mark the special occasion, a post appeared on the official Prince and Princess of Wales Instagram account. The caption was written by the three Wales children (plus Kate Middleton, aka "C"), and revealed their sweet nickname for the future monarch: "Papa."

Sweet message aside, in the comment section, fans were confused about one significant detail of the post...only Princess Charlotte featured in the image, while Prince George and Prince Louis were absent.

"And George and Louis?" one royal fan said in the caption, echoing what the rest of us are thinking. "Maybe they might post two other photos with them separately," someone else replied, adding, "Or they might have just loved this photo."

"Why is he only with Charlotte???" another royal fan queried. "Just an authentic family photo, I guess. It happens. Maybe the boys were busy monkeying elsewhere while this was taken?" a second follower replied. "Charlotte is better PR," theorized a third, as a fourth chimed in with, "Because she's the one who looks most alike."

Another follower simply responded with: "Why not?"

Elsewhere in the comments, fans couldn't help but point out the striking resemblance between Prince William and his daughter. "The Windsor twins!" one person said. "You and your mini me," wrote another.

Over on the official Royal Family Instagram account, which is typically where content relating to King Charles and Queen Camilla is posted, there was a poignant throwback photo to mark the day. "Celebrating all fathers, and thinking of those who wish they could be with their dads, today," the caption read, alongside an old image of Charles and his father, the late Prince Philip.

"Such a timeless and heartwarming tribute," a royal fan replied. "What a beautiful photo," added someone else.

Of course, there was a post to celebrate Prince William, too. A photo of both the current and future monarch was posted to the Royal Family Instagram Story, with the caption, "Happy birthday to the Prince of Wales!"