American crooner Tony Bennett has revealed he was diagnosed with Alzheimer's disease in 2016 but kept his condition quiet as he continued to work and tour.

The 94-year-old went public in a lengthy feature story published Monday in AARP The Magazine, the widely circulated periodical of the American Association of Retired People.

"Life is a gift -- even with Alzheimer's," Bennett tweeted, linking to the article.

The hitmaker with a cheery smile has had a particularly strong past decade career-wise despite his condition, becoming the oldest person ever to reach number one on the US album sales chart with his collection of duets with Lady Gaga.

The AARP article said a follow-up album with the pop star is set for release this spring.

"Singing is everything to him. Everything," said Susan Benedetto, Bennett's wife. "It has saved his life many times."

Bennett -- who trained in the operatic Bel Canto tradition and began his career in 1945 -- has continued to make music and sing at home to keep his brain stimulated with encouragement from his neurologists, according to the magazine.

The article references documentary footage of Bennett's sessions with Gaga, in which the singer appears at times "lost and bewildered."

US singer Tony Bennett, shown here on tour in 2019, was diagnosed with Alzheimer's disease in 2016
US singer Tony Bennett, shown here on tour in 2019, was diagnosed with Alzheimer's disease in 2016 AFP / Joseph Prezioso

Gaga appears aware of Bennett's condition, the article said, speaking in short, simple phrases that Alzheimer's researchers say are best for communicating with patients.

"You sound so good, Tony," she says at one point, to which he replies "thanks."

In one scene Bennett is described as appearing "utterly mystified about his whereabouts" before going on stage.

"But the moment he heard the announcer's voice boom 'Ladies and gentlemen -- Tony Bennett!'" he would transform into performance mode," AARP reports.

His last public performance was March 11 last year in New Jersey, before the pandemic halted touring.

"This has been a real blow from a cognitive perspective," one of his neurologists, Gayatri Devi, told the magazine.

"His memory, prior to the pandemic, was so much better. And he's not alone. So many of my patients are negatively affected by the isolation, the inability to do the things that matter to them," she said.

"For someone like Tony Bennett, the big high he gets from performing was very important."