Alan caused outrage when said he had 'no sympathy' for Robin after he took his own life.
He said: "I think it's just shocking. I don't have a lot of sympathy, I'm sorry… what you leave behind is diabolical. I'm really annoyed about that."
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But McFly singer Tom, 29, has blasted him in an open letter. Writing on his Tomclipated.com website, he said: "Sometimes… Alan, the storms come. I'm not talking about a light shower, I mean the full works.
"The darkest skies you have ever seen… It's so completely consuming that it is suddenly not only the only thing you know but the only think you have ever known."
Tom admitted that he is 'lucky' in the sense that his depression is 'mild and controllable', with the help of medication. Despite this, he revealed he still gets bad days.
READ: FIFI GELDOF REVEALS BATTLE WITH DEPRESSION: "I WEAR A PERMANENT MASK SO I WON'T BE JUDGED"
He continued: "The really weird thing about it for me is that when you're in the middle of that storm it's almost as it you don't want a way out of it.
"You are in too deep, what's the point in even trying to get out. Alan, it's as though no one understands… When I'm not in a storm I can remember pretty well what it was like being in it, but when I am in the storm I can't remember what it's like ever being happy.
"It's as if happy doesn't exist. The storm becomes your new normal."
The dad-of-one thanked those around him for understanding his illness and helping him through it.
But he said that people like Alan spouting words like 'selfish' 'diabolical' and 'no sympathy' does nothing to help those suffering from depression.
Although some are calling for Alan's sacking as a result of his insensitive comments, Tom disagrees.
"It was just very insensitive and unhelpful to publicly voice such a controversial view at that time so I think he should be poked in the eye and then send on some sort of educational course to open the eye we didn't poke to the world that I and so many people live in."