Robin Williams’ widow has said that his medical afflictions would have claimed his life within three “hard years” and that she does not blame him for his suicide. She said he was suffering from a rare form of dementia that my have caused him to suffer from a lack of reason.

Fifteen months after the actor took his life, Susan Schneider Williams told US media she laid the blame for her husband taking his life not on depression but on diffuseLewy body dementia.

In interviews with People magazine and with ABC News, she said: "It was not depression that killed Robin. Depression was one of let’s call it 50 symptoms and it was a small one.”

She added: “This was a very unique case and I pray to God that it will shed some light on Lewy bodies for the millions of people and their loved ones who are suffering with it. Because we didn’t know. He didn’t know.”

Susan Williams said the actor and comedian had been diagnosed with Parkinson’s disease, a progressive movement disorder, only a few months before his death, but that a coroner’s report found signs of Lewy body dementia, a difficult-to-diagnose condition that afflicts 1.4 million people worldwide and leads to a decline in thinking and reasoning abilities.

That may have contributed to the anxiety and depression for which he was treated in his final months, and probably played a role in his suicide by hanging, aged 63, in August 2014.

Although there were many reasons he ended his life, she said, it may have all come down to one: “I think he was just saying ‘No’. And I don’t blame him one bit.” She called him “the bravest man I’ve ever known”.

In pictures: Robin Williams 1951 - 2014 Show all 25 1 /25 In pictures: Robin Williams 1951 - 2014 In pictures: Robin Williams 1951 - 2014 Mrs Doubtfire Robin Williams with Sally Field in Mrs Doubtfire In pictures: Robin Williams 1951 - 2014 Oscar He won the Best Supporting Actor Oscar for 'Good Will Hunting' in 1997 Getty In pictures: Robin Williams 1951 - 2014 Mork and Mindy In Mork and Mindy, the TV series that launched his career in the 1970s Rex In pictures: Robin Williams 1951 - 2014 The Tonight Show On 'The Tonight Show with Jay Leno' in 2004. Williams was renowned for his hyperactive appearances on talk shows Getty In pictures: Robin Williams 1951 - 2014 Williams' hand and footprint ceremony Williams with two of his children, Cody (centre) and Zelda, and his wife, Marsha, during his hand and footprint ceremony outside the Mann's Chinese Theatre in Hollywood in 1998 In pictures: Robin Williams 1951 - 2014 Premiere of Old Dogs Robin Williams and his wife Susan Schneider at the premiere of "Old Dogs" in Los Angeles on 9 November 2009 In pictures: Robin Williams 1951 - 2014 Tour de France US cyclist Lance Armstrong chatting with US actor Robin Williams after he won the 91st Tour de France cycling race between Valreas and Villard-de-Lans on 20 July 2004 In pictures: Robin Williams 1951 - 2014 Annual People's Choice Awards Presenter Robin Williams speaks during the 35th Annual People's Choice Awards held at the Shrine Auditorium on 7 January 2009 in Los Angeles, California Getty In pictures: Robin Williams 1951 - 2014 The Big Wedding All star cast: Susan Sarandon, Robert De Niro and Robin Williams star in The Big Wedding In pictures: Robin Williams 1951 - 2014 Building homes Robin Williams Helps Build Homes With Habitat For Humanity, 4 December 2000 in Wilmington Getty In pictures: Robin Williams 1951 - 2014 Premiere of Man of the Year Robin Williams and wife Marsha Garces Williams arriving for the premiere of Universal Pictures "Man of the Year" at Grauman's Chinese Theatre in the Hollywood section of Los Angeles on 4 October 2006 In pictures: Robin Williams 1951 - 2014 CW, CBS And Showtime 2013 Summer TCA Party Robin Williams at the CW, CBS And Showtime 2013 Summer TCA Party on 29 July 2013 in Los Angeles, California Jason Kempin/Getty Images In pictures: Robin Williams 1951 - 2014 Holiday Troop Visit Robin Williams and US celebrity Lewis Black (L) laughing in the back stage during the entertaining performance of "Holiday Troop Visit" by US celebrities for Christmas at boardwalk stage of the Kandahar Air Field, Afghanistan on 16 December 2010 In pictures: Robin Williams 1951 - 2014 Andre Agassi's Grand Slam for Children press conference Robin Williams speaks during the Andre Agassi's Grand Slam for Children press conference at the MGM Grand Hotel, 2 October 2004 in Las Vegas, Neveda Getty In pictures: Robin Williams 1951 - 2014 Golden Globe Robin Williams holds his Golden Globe after winning for best actor in a comedy for his role in 'Mrs. Doubtfire' 22 January 1994 Getty In pictures: Robin Williams 1951 - 2014 Premiere of Happy Feet Two Robin Williams attends the Premiere of Warner Brothers Pictures' "Happy Feet Two" at Grauman's Chinese Theatre on 13 November 2011 in Hollywood In pictures: Robin Williams 1951 - 2014 Good Will Hunting Matt Damon and Ben Affleck pose with actor Robin Williams with their Oscars they won for 'Good Will Hunting' at the 70th Annual Academy Awards 23 March in Los Angeles Getty In pictures: Robin Williams 1951 - 2014 Mork and Mindy Robin Williams in 1980 with Pam Dawber, his co-star in the Mork and Mindy TV series Rex In pictures: Robin Williams 1951 - 2014 The Crazy Ones Robin Williams with his Mork and Mindy co-star Pam Dawber in The Crazy Ones series, 2014 In pictures: Robin Williams 1951 - 2014 Yankees versus Pittsburgh Pirates Robin Williams attends a game between the New York Yankees and the Pittsburgh Pirates during the Grapefruit League Spring Training game on 13 March 2008 at Legends Field in Tampa, Florida Getty In pictures: Robin Williams 1951 - 2014 Posing Robin Williams poses for a portrait during the 35th Annual People's Choice Awards held at the Shrine Auditorium on 7 January 2009 in Los Angeles, California Michael Caulfield/Getty Images for PCA In pictures: Robin Williams 1951 - 2014 Cecil B. DeMille Award Robin Williams holds his Cecil B. DeMille Award with award presenter Pierce Brosnan at the 62nd annual Golden Globe Awards show 16 January 2005 in Beverly Hills Getty In pictures: Robin Williams 1951 - 2014 Happy Feet Two Robin Williams laughs with Elijah Wood on arrival for the world premiere of the movie 'Happy Feet Two' in Hollywood on 13 November 2011 Getty In pictures: Robin Williams 1951 - 2014 Tony Awards Robin Williams speaks during the 65th Annual Tony Awards at the Beacon Theatre on 12 June 2011 in New York City Getty In pictures: Robin Williams 1951 - 2014 AFI Life Achievement Award honoring Mike Nichols Actor Robin Williams speaks on stage during the 38th AFI Life Achievement Award honoring Mike Nichols held at Sony Pictures Studios on 10 June 2010 in Culver City, California Kevin Winter/Getty Images for AFI

Williams starred in classic films such as Mrs Doubtfire, Good Morning Vietnam and Disney’s Aladdin. He won an Oscar for his supporting role as a psychologist in Good Will Hunting, which included a powerful speech delivered from a bench in a Boston park where fans this year marked the first anniversary of his death.

The actor’s symptoms began in November 2013, she said in an interview on ABC’s Good Morning America. They included stomach pain, constipation, urinary trouble and sleeplessness. By the following May, he was suffering from stiffness, slumping, a shuffling gait and “losing his ability in his voice,” she said.

In what would be the final week of his life, doctors were planning to send him to a facility for neuro-cognitive testing. But in that period he was “disintegrating before my eyes,” she said.