Prince Harry forced to up security measures after Greta Thunberg hoax

The Duke responded to the call from the Vancouver Island property he and wife Meghan are renting. Photo / WireImage

The Duke of Sussex has been forced to change his personal email address and phone number after inadvertently handing them to pranksters.

He was advised to take heightened security measures after falling victim to a hoax by Russian YouTubers who pretended to be Greta Thunberg, prompting him to wax lyrical on a range of issues from the difficulties surrounding his decision to leave the royal family to his disdain for President Donald Trump.

He was also duped into sympathising with the plight of a fictional island and offering to help rescue imaginary penguins from land-locked Belarus.

Buckingham Palace aides are hoping the humiliating prank acts as a "salutary reminder" of the dangers that lie in wait in his new life abroad.

The hoaxers succeeded in contacting the Duke after emailing an intermediary who appears to have forwarded it without any checks.

Under the heading "Call or meeting with Greta Thunberg", the messages purported to be from her director and were set up in the name of Ueli Maurer - the then president of Switzerland.

Harry has been forced to change his private details after he fell for a phone hoax. Photo / Getty Images

To the astonishment of the Russian duo, Vladimir Kuznetsov and Alexei Stolyarov, the Duke responded via his personal email from the property he is renting with the Duchess on Vancouver Island. He later called them without withholding his mobile number.

Royal sources said the success of the hoax served as proof of the vast amount of work undertaken behind palace walls to protect the family.

"As they move forward, they do need to invest in proper resources and have the right management, rather than adopting an approach more familiar in show business," one said.

The security breach came as the Duke and Duchess increasingly relied upon their US-based network of friends and advisers while shunning much of the counsel offered by their Buckingham Palace team, all of whom will lose their jobs at the end of this month.

The full audio versions of the two phone calls, made on December 31 and January 22, are expected to be released online tomorrow (Saturday) and are likely to include further embarrassing material.