Graeme Gibson, the Canadian author, conservationist and longtime champion of writers' rights, has died at age 85.

Margaret Atwood, Gibson's longtime partner, said in a statement Wednesday issued by publisher Penguin Random House Canada: "We are devastated by the loss of Graeme, our beloved father, grandfather and spouse, but we are happy that he achieved the kind of swift exit he wanted and avoided the decline into further dementia that he feared.

"He had a lovely last few weeks, and he went out on a high, surrounded by love, friendship and appreciation. We are grateful for his wise, ethical and committed life."

Gibson died Wednesday in London, England, where he had accompanied Atwood for the global release of her latest book.

Earlier this week, Atwood cancelled promotional appearances in Ottawa and Montreal for The Testaments — a sequel to her dystopian classic The Handmaid's Tale and one of this fall's most anticipated literary releases. The cancellation cited illness in the family.

A cover story in Time magazine earlier this month noted that Gibson was "living with dementia," and that Atwood juggled caring for him while working on her new novel. In a 2017 piece in The Walrus about the couple's love of birdwatching, Gibson confirmed he had been diagnosed with dementia.

Margaret Atwood and Gibson attend the 2018 Scotiabank Giller Bank Prize gala in Toronto. (Chris Young/The Canadian Press)

Born in London, Ont., in August 1934, Gibson penned novels (Five Legs, Communion, Perpetual Motion and Gentleman Death) as well as non-fiction, including Eleven Canadian Novelists (for which he interviewed his future partner Atwood), The Bedside Book of Birds and The Bedside Book of Beasts.

"We are deeply saddened by the death of such a beloved and distinguished author. Graeme was a friend to several generations of Canadian writers," Penguin Random House Canada CEO Kristin Cochrane said in a statement.

She hailed Gibson as "a true gentleman, whose gracious, elegant and witty manner touched all who knew him."

He was also an activist for different causes.

Gibson was a founding member of both the Writers' Union of Canada and the Writers' Trust of Canada, as well as a past president of PEN Canada. He was an advocate for conservation efforts and a devoted birder who helped found the Pelee Island Bird Observatory.

Gibson was invested as a member of the Order of Canada in 1992.

Along with Atwood, he's survived by, among others, their daughter Eleanor Jess, sons Matt and Grae from his previous marriage to publisher Shirley Gibson, and grandchildren.