Prince Harry celebrated his 37th birthday on Sept. 15 and as expected, the royal family members sent him well wishes through their respective social media pages. However, some noticed that Prince William and Kate Middleton's greeting was different.

Royal experts started to analyze Prince William and Kate's birthday greeting to Prince Harry and some found it cold. In fact, one said it was quite expected from the Cambridges due to the alleged growing tension between the two parties.

Royal expert Natalie Oliveri said on the "Today Show" that if Meghan Markle's husband was expecting a warmer birthday message from the royals, he, sadly, did not get that, per Geo TV.

Amid the many messages from the royal family, the one from the future King and Queen consort seemed to be a little curt. Usually, the couple would post a photo of the Duke of Sussex on his birthday doing his royal duties with them.

In fact, last year, they shared a snap of them, looking very happy during a charity race. A year before that, it was a photo from the royal wedding.

But now, it was only a simple "Happy birthday, Prince Harry" with his solo image, which many saw as quite cold compared to their previous birthday greetings. Oliveri believed it was a sign of the growing tension between the sixth in line to the throne and his family.

Despite that, though, it could never be denied that Queen Elizabeth II gave her grandson a warm birthday message, Cosmopolitan noted. She shared a collage of his photos on Instagram Stories and one of them even featured his wife, Meghan.

In the other two snaps, Prince Harry could be seen doing his royal duties. He was giving a young boy a high five in one while he seemed to be in a classroom and looked happy with a full grin on his face while talking to the kids in another.

In the caption, the Queen wished the Duke a happy birthday and added some jazzy birthday-related emojis. Of course, Prince Charles and Camilla, Duchess of Cornwall, also greeted their son by wishing him a happy birthday with a cake emoji and posting three photos of him-two with his dad.

For the finale, Prince William and Kate posted a solo picture of Prince Harry instead, smiling, and wrote a simple happy birthday greeting in the caption with a red balloon emoji. What made it different from other royal family members' greetings was that, it did not show him doing his royal duties when he was still an active senior royal family member.