In an interview with People, the 33-year-old actor reflects on how his film career skyrocketed and then was endangered when he became an alcoholic.
"I would have died, and I think about that every single day," he tells the magazine. "It got to the point where I was a fragile shadow of the young man that came into this business. Today, I'm the luckiest guy alive."
Klein was arrested twice for driving under the influence and served a jail sentence. During this dark period, he and Katie Holmes ended their relationship. He's currently been sober for nearly 19 months.
Klein first made a splash opposite Reese Witherspoon in the 1999 comedy Election and that same year starred in the ensemble hit American Pie, which became a popular film franchise. Its latest installment, American Reunion, hits theaters nationwide on Friday, April 6.