Like the man in the famous Milk Tray ads, it was "all because" he was trying to reach a woman he had the hots for.

But unlike the telly commercials, Robbie was in his birthday suit, blind drunk and incredibly horny.

The outrageous stunt has been revealed for the first time in a blistering new biography on the megastar.

Author Sean Smith tells of Williams' descent from a booze-loving teenager to a drink, drugs and sex addict - who could never say no to besotted girl fans.

He even risked death to get to one of his many groupie Angels - after discovering she was staying on the same floor as him, high up in the Loews Hotel in Monte Carlo.

Boozed-up Robbie - who bragged he was able to "sh*g anything I wanted to" - decided to surprise her by climbing on to her balcony instead of knocking on her door.

And it was certainly a shock for other guests and members of the public to see the famous singer dangling above.

Another time, Robbie's managers walked into his hotel room to find him hauling a topless girl in through the window. And his mate Coco Colcough recalled walking into their local pub in Stoke, Staffs, and seeing a girl with her hand down Robbie's TROUSERS.

Coco, who grew up with Williams, recalls in the book called Robbie: "I don't think he had a clue who she was." He added: "His eyes were, like, half open. He just sort of whispered, 'Whisky.' I said to this girl, 'Excuse me, love, do you mind if we just have a chat for a bit?' But she just carried on doing what she was doing."

One of the last girls to bed Robbie before he met his bride-to-be Ayda Field reveals how he struggled with his bipolar disorder.

Aspiring Hollywood actress Suzanne Coppin claimed that Robbie had a "chemical disposition to depression that he can't seem to attack. Obviously fame, money and anti-depressants can only eliminate it to whatever extent.

"It always haunts him." She tells how in their one night of passion Robbie was "really playful, really physical and kept pulling me on top of him. It was sexual, but not predatory."

Robbie's well-documented addiction to booze and drugs magnified his problems. The book reveals how, after leaving school, he and pal Lee Hancock would raid Robbie's mum's drinks cabinet - and fill an empty two-litre Fanta bottle with gin, vodka and whisky.

Lee said they'd get "rat-a*sed", adding: "We were big drinkers."

Troubled Robbie moved on to drugs - sniffing aerosol gas, inhaling amyl nitrate poppers and smoking dope. He took his first line of cocaine just before going on stage for the opening night of Take That's first arena tour, at Manchester's G-MEX.

Robbie's drugs habit got so bad, he imagined furniture racing around his bed. Worried pal Sir Elton John invited him to dinner at his Windsor mansion and warned him: "Stay away from the cocaine."

Robbie's emotional problems are traced in the book to his relationship with his dad Pete Conway, the former New Faces winner who walked out on his family to pursue a showbiz career.

And it credits Robbie's new bride Ayda for finally getting him on track.

The couple were set up on a blind date by actor Callum Blue - but Robbie failed to show. They eventually met at a party - and hit it off instantly.

Robbie was relieved to discover Ayda wasn't "some kind of hysterical Robbie Williams groupie".

A pal said: "He's smitten and the feeling's mutual."

When they tied the knot earlier this month, Robbie said: "I'm the happiest man alive. She makes me want to be a better person. And in the process, I have become a better person."
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