Highgrove House, Prince Charles' farming estate in Gloucestershire, has a specially-built panic room to protect the royals in case of a terrorist attack but it once accidentally trapped a prominent house guest, sending the Prince of Wales into fits of laughter.

In the documentary Secrets of the Royal Palaces, royal commentator Ingrid Seward said that Charles and his boys, Prince William and Prince Harry, had Tory MP Rory Stewart at Highgrove one time because he was also tutoring the princes. He excused himself to use the bathroom but then he ended up going inside the panic room.

Seward said that since the panic room was armor-plated, Seward didn't know how to get out. The residents of Highgrove had their training but the guests were naturally not aware of the protocols.

The MP had to shout at the top of his voice to be heard that he was trapped inside the panic room. Fortunately, Charles came down in his dressing gown, as he was comfortably resting, and eventually got his friend out. Seward said that the Prince of Wales then burst into laughter upon seeing Stewart's face.

Highgrove's panic room has never been used for its actual intentions but Charles had this built in the 1980s because the house was actually close to a busy main road and its brick walls were easy to climb. According to Ken Wharfe, a former royal security expert, the IRA was making threats to Charles's life at that time so the royal turned Highgrove into "Fort Knox," as historians said.

The Prince of Wales had valid reasons to fear for his and his family's safety since his uncle, Louis Mountbatten, was assassinated by the IRA. Royal commentators said that it wasn't farfetched that Charles was also on the hit list of the terrorist group so they had to secure his favorite home.

Aside from the panic room, Highgrove has security cameras, ground sensors and a roaming police officer. According to the experts, the security measures at Highgrove are so discreet but effective.

Meanwhile, the panic room is stocked with everything the royals need if they were actually under threat, according to Hello! There are provisions for food and drinks, as well as radio transmitters and the necessary weapons. There is also a set of containers for Charles and his family's blood group, in case of an emergency. If Highgrove House is destroyed, the panic room is expected to remain intact because it is lined with steel.