Previously, Berman had published two editions of a book "Perfect Spy – The Incredible Double Life of Pham Xuan An" which served as the basis for a 32-episode television documentary on the late intelligence general.

On the website –http://perfectspyx6.com/– the historian also shares talks between the Vietnamese spy and himself made during the process of writing the book.

Pham Xuan An was born in 1927 in southern Dong Nai province and died in 2006.

During his double life as a secret agent, An, whose alias was X6, worked for the intelligence group H63 in Saigon, which was later renamed Ho Chi Minh City.

He was a strategic agent and played an important role in the resistance war against the American invaders. Anwas also a reporter for Reuters, Time magazine, and the New York Herald Tribune and received several honours from US politicians and the media.

He befriended everyone who was anyone in Saigon, including American journalists such as David Halberstam and Neil Sheehan, the CIA's William Colby and the legendary Colonel Edward Lansdale, not to mention the most influential members of the South Vietnamese government and army.

No one ever guessed that he was providing strategic intelligence to Hanoi, smuggling invisible ink messages into the jungle inside egg rolls.