Britain's Prince William paid a secret visit to Government Communications Headquarters (GCHQ) in Cheltenham, Gloucestershire on Thursday (19.03.15).

Prince William

Prince William

The 32-year-old royal, who is currently preparing for the birth of his second child with the Duchess of Cambridge, travelled to Britain's most secretive building, where he was shown how the communications of suspected terrorists and foreign spy agencies are tracked.

A GCHQ spokesman said: "The prince paid a visit to GCHQ on March 19. As it was a private visit, we cannot go into the details of his itinerary."

Meanwhile, a spokesperson for Kensington Palace confirmed the visit had taken place, saying it was a "private visit" taken in an "official capacity".

She added: "The travel costs for it will fall within the official Royal Travel budget."

Elsewhere, an eyewitness explained that the royal turned up in a helicopter.

The onlooker told the Daily Telegraph newspaper: "William was dressed casually in a shirt and V neck sweater and what looked like beige chino trousers.

"We guessed it was going to be a member of the Royal family on board when we saw the helicopter, but it was quite a surprise to see him."