EXCLUSIVE: Keith Urban's Shocking Drug Use Revealed — Former Writing Partner Claims Singer Once 'Snorted $320K Worth of Cocaine'... as His Wild 'Binges' Resurface Amid Split From Nicole Kidman

Keith Urban's dark past has resurfaced following his split from wife Nicole Kidman, as his former writing partner claims the singer once snorted thousands in cocaine, RadarOnline.com can reveal.

The Somebody Like You hitmaker's former friend and songwriting partner, Vernon Rust, is pulling back the curtain on Urban and his shocking behavior.

Rust, in his new memoir, Fake News, claims he and Urban once snorted $320,000 worth of cocaine in the late 1990s during an "epic" multi-day binge.

"We lived in the studio," Rust, who also spent years hooked on cocaine, writes. "We did a lot of coke, and stayed up for days." According to Rust, the country singer also used "coke, crack, and weed."

However, before Rust hit bookshelves, he was already talking about his past with Urban after meeting him in Nashville, Tennessee, in 1993, and working together.

"We became friends, then best friends, then we became freakishly inseparable. We spent all our hours together,” Rust previously recalled.

However, while working with The Ranch, Urban's now-defunct band, for their self-titled 1997 album, Rust said drugs were "just there," and claimed, "We all got into it. Keith more than anyone."

He added: "Keith's thing was crack, and lots of it. He was the big rock star, so he always got the first pick of the drugs when they turned up. He'd take a rock for a hit, then take more and hide them in his pocket or somewhere. He'd go off on benders, and someone would find him in a crack den curled up in the fetal position."

Rust claimed Urban would "take the hit and crawl under beds, crawl across roofs, walk off..."

When Urban and his now-estranged wife Kidman met in 2005, the former American Idol judge was believed to be heavily involved in drugs and alcohol. Following their wedding, Urban did a three-month stint in rehab, launched by Kidman, a decision he said changed his life forever.

"That's the point right there, where she really should've just walked," Urban told Oprah Winfrey in 2010. "I'm just so glad she didn't, and she made a decision to turn around and initiate, ultimately, this intervention, and it was done in such a way that the love in that room at that moment was just right. I was like, 'Put the cuffs on, let's go.'"

Urban later told Rolling Stone: "I was very, very blessed to have Nic call an intervention on me. I had a tight group of friends around me for the intervention. And off I went."

Before Kidman stepped in to help, Urban told the publication he "wasn't in any recovery program of any sort. I wasn’t in AA. I didn’t have a sponsor. I didn’t have anything. Meeting Nic and falling in love with Nic and starting a relationship with Nic became – I realize now in hindsight – my sobriety."

"That was how I was able to keep it together," he said at the time.

The movie star later told Vanity Fair: "I'm more than willing to walk it with him." And Kidman sounds like she's in it for the long haul with Urban, as she is said to still want to be with him despite the "separation."

Kidman, 58, filed for divorce late last month, citing "irreconcilable differences," after futilely fighting to save the pair’s rocky romance, sources claimed. According to reports, their prenuptial agreement includes several unorthodox clauses, like a "cocaine" clause, which notes Urban would be in line for $600,000 from the Oscar winner for every year they were married, which amounts to just over $11million.

The only catch? Urban would have to say no to drugs and alcohol.

Amid the chaos, the music star is already believed to have moved on with other women following their split, with sources linking him to his female guitarist, Maggie Baugh.