Michael Palin says he and the other members of the Monty Python comedy troupe will rally around Terry Jones as he battles dementia.
Palin, 73, presented Jones, 74, with a Bafta Cymru award for his contribution to film and television at the weekend.
Welsh-born Jones is suffering from primary progressive aphasia, which is a form of dementia that affects his ability to communicate.
Palin told the Radio Times he had been aware Jones's memory was failing for a number of years.
He said: "This is progressive and the loss of the ability to speak is one of the things it brings.
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"I grew up with a father who stammered and that was difficult enough for him. But for words just not to even be there, not to utter anything, it's a terribly sad thing to befall anyone.
"I saw John (Cleese) yesterday and there's nothing much we can do but stand there and say, 'Oh God, what has happened to our friend?' But the Pythons will rally round."
Palin and Jones were members of the famous group, which also included Cleese, Terry Gilliam, Eric Idle and Graham Chapman, who died in 1989.
Jones directed Monty Python's Life of Brian and Monty Python's The Meaning of Life. Alongside Gilliam, he co-directed Monty Python and the Holy Grail.
In 2014, the remaining Monty Python co-stars reunited for a series of live shows at London's O2 arena.
