"I'm not going to eat or drink. What do you think?" That was the question bestselling author and vet Bruce Fogle's mother put to him when she decided she wanted to end her life.

Aileen Breslin was 100 and as sharp as a knife mentally, but her body had given up on her after a second hip replacement operation in Toronto last year left her immobile, and doctors said she couldn't be rehabilitated.

She was in constant pain, and didn't see a reason for carrying on.

Bruce, 71, who's penned a plethora of bestselling books on animal behaviour, had dealt with plenty of life or death situations involving animals, but never one involving a close relative.

"'Of course,' I answered, 'If you don't eat or drink, you'll die. And I don't want you to die, but it's your choice and I'm not going to interfere'," he explains.

He advised her to continue taking fluids, recommending that she drank water, tea or coffee, which didn't contain any calories. His mother had been having her daughter-in-law's chicken soup, which she enjoyed. Bruce told her that was fine if that's what she wanted, but chicken soup would make her live longer.

"At that point, I thought that if she stopped eating and drinking, she'd probably live for two weeks, but I forgot that she hadn't been eating at the hospital for almost three weeks."

She passed away a few days later, in December last year.

"She was very lucid to the end, to the point where she made the decision that her life was going to end. She passed away, I'm happy to say, through choice."

The Canadian vet, who has lived in England for 45 years and is married to actress Julia Foster, didn't go through inner turmoil about his mother's decision, but did feel anguish that he couldn't do more to help.

"My turmoil was that I couldn't help her. I would have wanted to give her a bottle of phenobarb' [sedative] tablets, and I started thinking, 'How can I get her something?'

"One of her nephews came to visit and she was very tired on the day. He's a pharmacist and I asked him how pharmacists kill themselves and he told me the drug, which is a very simple drug and easily available on prescription. I thought maybe I could get a bit of that.

"When he left, my mother called me over with her finger and she said, 'Did you write that down?' She'd been lying there listening to everything. I did have some turmoil that I couldn't legally help her. I decided against it, because I knew that in Canada, it would be murder.

"I didn't feel any emotional distress that she was going to die, because I understood why she wanted to die," he continues. "She was 100, and the words she used were, 'I'm all used up'."

Bruce's latest book, Barefoot At The Lake, is much more than a childhood memoir.

It charts the summer of 1954, when he escaped to the family cottage at Lake Chemong in Ontario with his parents and siblings, where he realised his deep connection with nature.

But it's also an homage to his mother, and has helped him remember her as the person she was back then; a sassy, sexy, gregarious woman with a zest for life, who didn't realise how attractive she was.

"Now I think of this sexy woman, full of vitality, who didn't know she was sexy, but every man who walked by turned round to look at her."

Before he sat down to write the book, Bruce recalls that he and his siblings had started to tire of Aileen's 45-minute monologues, consisting of a stream of moans and groans.

"We were getting tired of our 99-year-old mother talking about her aches and pains, how difficult life was because she'd been an active woman and now could no longer knit or sew. If she watched television, it had to be out of the corner of her eye at an angle. She found life very frustrating. She'd developed arthritis after being an industrial walker. At 95, she had been walking five miles a day at speed.

"As I started writing, my mother in her late 30s came back into my mind. I found that very gratifying. My brother and sister can't do that yet."

Aileen had her first hip replacement at 98. Two days after the operation, she was walking with a frame, Bruce recalls. Then, when she turned 100, she broke her other hip and had that one replaced too, but this time, she didn't recover.

It was three weeks later that she asked her son to support her decision not to eat or drink.

His memoir was already written and he read the entire book to her in hospital.

"She loved it because it brought back all the memories. It's written in very short vignettes, so I could read one or two to her and that would set her mind off on a tangent. It revived all these memories. Of the various places she lived during her life, that cottage has been a constant. That was her home."

Five generations have enjoyed the cottage in Ontario - which Bruce's father built and which the family still owns - including his broadcaster son, Ben Fogle, and his family.

Aileen corrected her son on some accuracies, but he gently argued that it was artistic licence and that some events may have not been in chronological order.

Before she died, and when the family had accepted Aileen's decision without question, Bruce asked her what she wanted him to say at her funeral.

"Her answer was, 'Well I heard all the accolades at my 100th birthday so you don't have to do a eulogy, they were all wonderful'."

He then asked her if she had any advice for him.

"She said, 'Be happy with what you've got'."

And you get the impression he is.

:: Barefoot At The Lake by Bruce Fogle is published by September on April 30, priced £14.99