By Karen S. Schneider
Updated August 28, 2006 12:00 PM

No one paid much attention to the two old friends sitting outside chatting in early August. At the rehab center, Robin Williams was just another guy trying to get sober; Lance Armstrong another pal taking advantage of family day to offer encouragement. During their hour-long visit, says Armstrong, “I asked him, ‘What is it that we need to do as friends [to support you]?’ He said, ‘I just need to be more mellow'”—that is, to slow down what Armstrong calls Williams’s “natural need to do everything times 10.” Armstrong pressed on to ask if there was anything specific he could to do help his longtime biking buddy. “I asked, ‘Should I not drink in front of you?'” says Armstrong. “He said, ‘No, not at all. This is a job for the individual with the problem.'”

Until recently, very few people knew Williams was again battling a problem. But two decades after he swore off alcohol and cocaine, Williams, 55, checked himself into a rehab clinic—with the support of his wife, Marsha, 50, their kids Zelda, 17, and Cody, 14, and Zach, 23, his son from his first marriage. According to an Aug. 9 statement by his publicist, Mara Buxbaum, Williams “found himself drinking again and has decided to take proactive measures to deal with this for his own well-being and the well-being of his family.”

For a man so outspoken about the perils of his past substance abuse—”a living hell,” as he put it—the announcement was a stunner. “We were all shocked,” says one close friend. So, too, were acquaintances at the nightclub Urban Well in Vancouver, where Williams filmed RV last summer and often showed up to do last-minute stand-up shows. “When people wanted to buy him a drink, it was Coke or nonalcoholic beer,” says one employee. “He never drank alcohol.”

So what went wrong? Several sources close to him dismiss speculation of marital trouble. His family is with him “absolutely,” says one. Nor, notes a colleague who has worked with Williams on several projects recently, does he believe he has been drinking for long: “There was no sign of a problem [on the sets]. He was a complete professional, gracious and thoughtful; a joy to work with.”

While some observers noticed that Williams seemed weary after filming three back-to-back films (including the current The Night Listener), Armstrong, like other friends, says there was no one event that set Williams off: “He was not spiraling down fast.” Actor Harvey Fierstein, who has been exchanging e-mails with Williams since the news broke, offers the perspective of a friend and fellow recovering alcoholic: “Robin is incredibly generous, loving and smart, but he’s very human.” And as Fierstein points out, a relapse is often as simple as letting down one’s guard. “The longer you stay sober the harder it becomes because you forget,” he says. “Suddenly you’re thinking, ‘I was under a lot of pressure then and now I’m not.’ Whatever, it’s all denial. I’m just happy it wasn’t worse, like Mel Gibson acting out or John Belushi overdosing.”

It was, in fact, the death of Belushi that helped scare Williams sober in 1982. While starring on the hit ABC sitcom Mork & Mindy, Williams succumbed to fame’s temptations—cocaine, in particular. “Most people get hyper on coke. It slowed me down,” Williams told PEOPLE in ’88. “It made me withdrawn. And I was crazy back then—working all day, partying most of the night. I needed an excuse not to talk.”

Williams had spent time with Belushi hours before the Saturday Night Live comic overdosed on heroin and cocaine at the Chateau Marmont. The demise of a man Williams considered “the strongest, a bull with incredible energy” was, he said, “frightening.” At the same time, his wife, Valerie Velardi, was pregnant with their son. As Williams said, “I knew I couldn’t be a father and live that sort of life.”

And so he went clean, cold turkey. Not even the sensational breakup of his first marriage in 1988—after separating from Velardi he moved in with and a year later married Marsha Garces, Zach’s former nanny and at the time his assistant—tested his sobriety, friends have said. In Garces, he told the Chicago Sun-Times, he found “my soulmate”—and in fatherhood to Zach, Zelda and Cody, his calling. “There are days when I look at my kids playing and I think, ‘This is heaven,'” Williams said. “It’s not just contentment, but a power surge in your heart.”

Today, he can rely on that power—from family as well as friends—to help him through this tough time. “He has a helluva lot of people cheering for him,” says Armstrong. “I’m very optimistic.” So is Fierstein. “Robin will be all right. He did something really smart,” he says. “He asked for help.”