Chris Packham has spoken of having feelings that twice pushed him to the brink of trying to take his own life during severe bouts of depression.
Chris, 54, revealed he was diagnosed with Asperger's Syndrome in his 20s and described his thoughts as a "great, hopeless vacuum".
The naturalist, who presents the BBC Springwatch, Autumnwatch and Winterwatch programmes, spoke of his difficulties in an interview with The Times and in his new memoir, Fingers In The Sparkle Jar.
He said: "I have been severely depressed, yes. I nearly killed myself twice."
One crisis came in 2003, at the age of 42, when he "didn't have enough drugs to be sure it would work. I wouldn't want to make a bad job of suicide".
He chose not to go through with it as he did not want to leave behind his two dogs or hurt his family, he said.
In his book he rubbishes the idea that suicide is selfish, saying: "Selfishness would only be apparent if you could be conscious of your actions' effect on others. But there are no fucking others, they are not there. There is nothing there ... but you and a fucking great, hopeless vacuum."
Chris, who lives in the New Forest and is in a relationship with the owner of the Isle of Wight Zoo, Charlotte Corney, also described being bullied mentally and physically as "the weird kid" when a teenager.
He told the newspaper: "I didn't understand that I was different. I didn't understand why I was being rejected. I didn't get invited to parties. I didn't fit in."
Chris, whose sister Jenny Packham is a favoured fashion designer of the Duchess of Cambridge, says he has no friends but is close to an ex partner and her daughter.
The preservation of the natural world is still an overriding passion and he is firmly against fox-hunting, saying that killing something for pleasure has a "psychopathic element" to it.
And while he believes climate change has come more into the public and political conscience in recent years, those in power still need to be better-educated before issues are adequately addressed.
He said: "There will be catastrophes - floods, mainly - then we'll buckle up and get it sorted."