Michael Palin says Terry Jones no longer recognizes him due to his dementia.
The pair became close friends during their time in the Monty Python comedy troupe with Terry Gilliam, John Cleese, Eric Idle and the late Graham Chapman but Jones' dementia has progressed so much that he no longer knows his old pal.
Speaking to The Sunday Telegraph, Michael, 76, said: "The last time I saw him I don't think he recognized me. We knew each other well. It feels like a part of yourself isn't there any more."
However, Michael can still see flashes of his old friend and was delighted when he read Jones some extracts from their book 'Dr Fegg's Encyclopedia Of All World Knowledge' and Terry only laughed at his own jokes.
Michael said: "At a certain moment Terry began to really laugh, the way he used to laugh.
"That was a great moment. But what made it so wonderful was that he only laughed at the bits he'd written. And I thought, 'that shows there's a bit of Terry still there'."
Meanwhile, Gilliam, 78, recently insisted that 'Monty Python' is "dead" due to Jones' dementia and the remaining members have no plans to revive it.
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He said: "It's dead, I think. There are only four of us who can actually function. It depresses me so much because he's not there. It's just very sad."
Jones, 77, was diagnosed with Primary Progressive Aphasia, a form of frontotemporal dementia (FTD) that impairs the sufferer's ability to speak and communicate, in 2015 and Palin previously admitted it is difficult to see his friend suffering.
He said: "He's still around, he's not disappeared, quite apart from the wonderful work that he left behind, the work he's done. There's still a bit of Terry there, the sparkle in the eye. He can't communicate, that's the problem, which is so ironic for someone who loved words and debate and jokes and opinions and ideas.
"There's enough of Terry there to make me feel grateful that I can still go and see him."
The surviving members of Monty Python reunited for 10 live shows at The O2 arena in London in 2014, and it was then that the rest of the group could see Jones was having problems performing.
Jones' family - including his partner Anna Soderstrom - went public with his condition in September 2016 to raise awareness of FTD, which, unlike Alzheimer's disease, does not result in a loss of reasoning.
However, decision-making and speech are affected and sufferers often seem less caring.