Prince William’s 21st birthday took a turn for the worse when palace security allowed an uninvited guest into the celebration. The milestone occasion turned into a heated confrontation when the Duke of Cambridge came face to face with the party crasher.

Before William was taking on senior royal duties, he was a young man who was looking forward to having a good time. For his 21st birthday, the Prince threw an “Out of Africa” theme bash at Windsor Castle.

According to the Channel 5 documentary “Royal Scandals,” Aaron Barshak, who was dressed up as a “comedy terrorist,” managed to slip past security and get into the party.

“Of course, trying to monitor who’s meant to be there and who’s not meant to be there, when everybody is dressed in ridiculous outfits, does make it harder for the security services,” royal expert Daisy McAndrew noted.

“However, the comedian was dressed in a pink dress and a fake beard, so he clearly didn’t fit with the theme. He should’ve set security alarm bells going much earlier than he did,” she added.

After slipping into the soirée, Barshak interrupted Prince William’s speech and planted a kiss on the birthday boy. “No-one realized anything was wrong until Prince William looked at him and said: ‘Who the hell are you!’” Royal biographer Katie Nicholl revealed.

The unexpected interruption caused many to question whether the Royal Family was being properly protected. “Security breaches don’t get any bigger than that. It was a huge royal scandal, suddenly all of the attention was off the birthday and what was essentially a massive security threat,” the author explained.

“Every senior member of the Royal Family was in attendance. Had that been a real-life terrorist, we’d be talking about a very different story today.”

Since then, the palace has continued to take precautions to ensure the safety of the Royal family.