Prince Harry has left royal fans surprised after they realised his real name isn't Harry at all.

As the Duke of Sussex marks his 40th birthday today (Sunday, September 15), fans have flocked to social media to send greetings, while others have uncovered the truth about his official title.

Harry's birth certificate actually reads Henry Charles Albert David, and his children's birth certificates also list this as his real name. Like other members of the Royal Family, he doesn't have a fixed surname like most of us and used 'Wales' during his younger days before switching to Sussex and Mountbatten-Windsor.

Astounded social media users have taken to X (formerly Twitter) to express their shock. One wrote: "PRINCE HARRYS REAL NAME IS HENRY?? wtf," while another agreed: "PRINCE HARRYS REAL NAME IS H E N R Y?"

"I just learned Prince Harry (or anyone in the royal family) does not possess a last name, nor born with one. Wild," said a third, while a fourth wrote: "Prince Harry isn't called Harry?!"

Even the duke himself has poked fun at his name. Speaking at the WellChild Awards earlier this year, he said: "My name is Henry, but everyone calls me Harry. I have no idea."

While most of us now use Harry as a standalone name, it was originally a nickname for Henry and can be traced back Medieval England.

The Telegraph previously reported went by the name Captain Harry Wales during his military service. At the time, his father, King Charles, was the Prince of Wales.

He also adopted the surname Mountbatten-Windsor, following Queen Elizabeth II's decree that any Royal requiring a surname could use this one.

His children, Archie and Lilibet, also bear the surname Mountbatten-Windsor, which is included on their birth certificates, along with their middle names, Harrison and Diana.