Actor Timothy West has told how his wife, Fawlty Towers star Prunella Scales, has been suffering from "a sort of mild Alzheimer's".
Stage and screen actor West, 79, talks about Scales' condition in a new More4 documentary, Grand Canal Journeys.
The actress, now 81, is best known for her role as Basil Fawlty's wife Sybil in the comedy Fawlty Towers but has continued to notch up screen roles .
West, who last year appeared in Coronation Street and has since joined EastEnders, tells the programme, which is broadcast later this month, that Scales suffers from "a sort of mild Alzheimer's", the Radio Times said.
The couple have been navigating Britain's canals on a slow boat ever since they first sparked a passion for the hobby when they borrowed a friend's boat for a fortnight in the 1970s.
And West tells the programme, in which the pair embark on four canal journeys across Britain, that the journeys are perfect for his wife because of the difficulties with her memory.
"She can't remember things very well, but you don't have to remember things on the canal," he says.
"You can just enjoy things as they happen - so it's perfect for her."
Scales says that she was determined not to let the condition keep her from the stage.
"I always say I want to die on the eighth curtain call," she says.
"Eight will mean the show's been rather a success. I just hope I'm somewhere near the middle and have been reasonably good in the part."
The pair celebrated their golden wedding anniversary last October with a trip down the River Thames on paddle steamer the Waverley.
After Henry star Scales says of her hobby: "It's always Tim who steers! But I enjoy running up and down because of the wonderful wildlife on the towpath. And it keeps you fit."
Alzheimer's Society's director of external affairs, Dr Alison Cook, said: " Alzheimer's Society would like to thank Timothy West for speaking out about his wife Prunella Scales' dementia and raising awareness of the condition.
"Their recent adventure navigating Britain's canals shows that it is possible to live well with dementia and plan to carry on enjoying life.
"We would urge anyone who is concerned about themselves or a loved one to speak to their GP today or contact Alzheimer's Society for advice and support."