Jeff Todd, who helped Porter write "The Man Behind the Bow Tie,'' said Porter died early Wednesday at a hospital in Panama. He was 59.
Todd says he was informed of the death by Porter's friend and physician Dr. Karol Sikora. Porter had been battling lung cancer.
"I knew he was in hospital and I would hear little things here and there about what was going on with him," Todd said Wednesday.
"I guess I had a feeling this was going to happen. But it was almost a superhuman quality that (he developed) through this because he did fight it for so long."
Sikora said in a statement that Porter's death was sudden, and that doctors thought the oncologist would live for another two or three weeks. He died alone.
Todd said Porter -- who had been battling the disease since December 2012 -- was released from detention in the Central American country six weeks ago to undergo treatment.
He was the former head of the McGill University Health Centre and was once appointed by the prime minister to head the Security Intelligence Review Committee, a CSIS watchdog group.
In joining SIRC, Porter was also sworn to the Privy Council. He was elevated to SIRC's chair two years later but resigned in December 2011 following published reports of his business links to an international arms dealer.
After moving to the Bahamas, he was arrested along with his wife, Pamela, during a flight layover in Panama.
Porter had been detained since May 2013 in Panama as he fought extradition to Canada.
Police allege that he accepted a bribe of several million dollars from former executives of SNC-Lavalin for awarding the firm the contract for a hospital project, but Porter denied committing any fraud.
The McGill health centre issued a brief statement on Wednesday extending condolences to Porter's family — he leaves behind his wife and three daughters.
Pamela Porter was sentenced in December to 33 months in jail after she pleaded guilty to two counts of money laundering in connection with her husband's case.
Todd called Porter's death on Canada Day "stranger than fiction" because of his highly publicized standoff with the Canadian authorities for extradition.
"It's a poignant end, for sure," he said.
"I don't know how you take it, but it's definitely poignant."
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