Camp and cuddly, celebrity astrologer and Strictly Come Dancing star Russell Grant has always been a colourful character, firstly in those multi-coloured sweaters on BBC Breakfast Time back in the Eighties, and later in sparkling sequins on the nation's favourite dance show.

"I think colour is so important in our life," the ebullient entertainer enthuses, as he tells me about his latest venture, an adult colouring book called Russell Grant's Art Of Astrology.

"I've always had a penchant for colour and when I'm in an SAD [seasonal affective disorder] mood, especially with the terrible weather we're having, I've always found myself needing light and bright. I need the yellows!"

Behind his bright and breezy persona there have been much darker times, when great storm clouds of depression hung over him following the death of his two grandmothers, which reportedly led him to become a suicidal recluse.

"That's a bit drastic," the 64-year-old entertainer reflects. "As I said at the time, you get to a point where you don't see any way out, so what you do is contemplate what it would be like to get out of here. Then reality hits you and you realise it's a selfish act, because you leave all those people who love you - and why would you do that?

"We all reach lows, but I wouldn't ever say I got to the point of actually thinking, 'I'll go and buy the pills'. But you look up and think to yourself, 'There's got to be something better than this'."

His weight ballooned from 2005, as he comfort-ate to assuage his grief, gaining 10 stones to reach, at under 5ft 8ins-tall, an alarming 27 stones. Binging on chocolate and cheese and popping anti-depressants, he admits it was his worst period.

"I'd lost my two grandmothers - one who I'd nursed and cared for who had Alzheimer's, and the other who I was very close to and who I spent most of my time with when I was a teenager.

"To lose two people who are very dear to you triggers an emotional blast, which is what I went through. It was a colourless time. You can't see any hope and there's no light at the end of the tunnel."

The weight gain led to further health problems, including several heart scares, prostate problems and Type 2 diabetes. He could barely get out of bed, let alone think about exercise. But it led him to take part in TV's Celebrity Fit Club in 2006, which saw him lose four stones, only to put it back on again.

Sheer willpower pulled him through, he reflects.

"January 5, 2009 was the date I decided to take control of my life. I'd got through a very bad Christmas and reached the point where I couldn't wipe my bottom. It's getting to a bad state when you have a blue badge on your car and a stick because you can't walk. It was a wake-up call - you either go under, or you build yourself up."

He had become a hermit in his home in Snowdonia, seeing no one except Doug Beaumont, his manager and long-term partner.

"I had to do something I loved, which was returning to performance and acting."

First he got a job directing a production of A Midsummer Night's Dream at Portmeirion. He lost five stones in five months. Then in 2011, he received the call to do Strictly - and soon became the nation's sweetheart again, gaining a host of younger fans in the process.

"By then I was losing weight. When I did Strictly, I lost seven inches around my waist and got down to 16 stones. I'm 16-and-a-half now, so I've kept the weight down.

"I keep in touch with Flavia [Cacace, his Strictly partner] every day. We send each other notes all the time. She's the most wonderful woman. And I'm still dancing. I go on P&O cruise ships now for Strictly and teach samba, salsa and cha cha cha.

"The way I get out of low moods is by putting on music - Sixties disco," Grant continues. "That was my therapy. I was dancing like crazy long before Strictly. I'd put on Kylie's Step Back In Time and it was like a cardio workout to help me lose weight.

"When Flav and I were dancing to Better The Devil You Know, Kylie sent me a note saying, 'Shimmy, Russ!' It was just fabulous."

Born in Middlesex, the son of a set designer and secretary, Grant went to stage school, soon landing roles in TV sitcoms, including On The Buses and Doctor In The House.

Astrology was a sideline - until the late Queen Mother visited his stand at the Ideal Home Exhibition, raising his profile and gaining him a TV slot in the process. But acting has always been his first love.

He's not stopped working since 2011, making numerous appearances on Strictly spin-off It Takes Two, as well as a documentary about his early life, nine West End shows and a stint at the Edinburgh Festival.

Then there's the cruise ship work, too.

"When I was on the Britannia last summer, they were expecting 30 or 40 people, and 350 turned up. People's reaction is positive. It's been the most incredible time of my life.

"I've also got a dad who's 88 and a mum who's 88 and they don't live together, but let me put it like this: I have to make sure they're OK."

He still has his house in north Wales but now lives near London, where the work is.

One of his reasons for continuing work is Alzheimer's, a cause close to his heart. He helped care for his grandmother, Nanny Alice, for some years before she died from the disease.

"The day I retire, my darling, is the day I give everything up. When you have someone in your family who suffers from Alzheimer's and dementia, you realise you have to use the brain like a muscle."

He now devotes a third of his working life to supporting the charities Alzheimer's Research UK and Dementia UK, too.

"Of course I worry about getting dementia. In the 1980s, when my nan first showed symptoms, you have no idea what it was like trying to get help. It was terrible."

He doesn't want tests to assess if he is likely to get dementia.

"There's no cure, so what's the point? That would be foolhardy. I don't want to worry myself to death."

Looking at his workload, he surely doesn't have a lot of time to consider his own fate. With a West End play, a pilot for a new astrology show in the US and his first novel - working title 50 Shades Of Pink - on the cards, his feet are hardly touching the ground.

:: Russell Grant's Art Of Astrology is published by Blink, priced £9.99