Daniel Ellsberg, the military analyst turned public interest witness who brought to light the so-called Pentagon Papers, exposing the lies told by the armed forces and successive US administrations about the Vietnam War, announced Thursday that he was recently diagnosed with terminal pancreatic cancer stage.

“On February 17th, almost without warning, I was diagnosed with inoperable pancreatic cancer,” Mr. Ellsberg, 91 today, explained on Twitter in a letter he had initially sent only to friends. “I regret to inform you that the doctors give me three to six months to live,” reads the text.

The Pentagon Papers (officially known as the Report of the Office of the Secretary of Defense Vietnam Task Force) were a multi-volume, top-secret study of how the US became embroiled in the bloody stalemate that was the Vietnam War.

The disclosure of parts of this study caused a huge scandal in the US, because the text was in complete contradiction to both what the Pentagon announced publicly and the government’s assurances about this war for years.

In 1971, Daniel Ellsberg, then a US government adviser who helped write the study, leaked parts of it to the New York Times and other newspapers.

Their publication profoundly changed the public debate, overturning what had been taken for granted about the evolution of the armed conflict. They documented, among other things, that one US administration after another increased the scope of military involvement, even though it was clear that the US could not win this war.

Following the revelations, the US Department of Justice brought criminal charges against Mr Ellsberg for leaking the contents of the study to the media. But the charges against him were dropped in 1973, following a mistrial in 1972.

Daniel Ellsberg, who will turn 92 in April, has been a human rights defender and anti-war activist for decades.

He stressed that he decided not to undergo chemotherapy and added that he has “excellent” care when he needs it.

Despite his diagnosis, Mr. Ellsberg assured that he is pain-free and will continue to give interviews and deliver seminars digitally.