His voice breaking, McGwire says, "It's the first time they've ever heard me, you know, talk about this. I hid it from everybody."
During a 20-minute phone call Monday, McGwire says he called commissioner Bud Selig and Cardinals manager Tony La Russa earlier in the day to personally apologize.
McGwire says that when he used steroids, he never imagined he would have to talk about it to national media.
In his AP interview, McGwire's voice shook when he recounted breaking the news to his son, Matt, who is 22. When McGwire hit the record homer, he hoisted Matt - then a 10-year-old batboy - at home plate. The former player called that conversation the toughest task in the ordeal.
"He's very, very understandable. So are my parents," McGwire said. "The biggest thing that they said is they're very proud of me, that I'm doing this. They all believe it's for the better. And then I just hope we can move on from this and start my new career as a coach."
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Mark McGwire's full statement:
Text of the statement Mark McGwire issued Monday, admitting he used steroids during his career:
"Now that I have become the hitting coach for the St. Louis Cardinals, I have the chance to do something that I wish I was able to do five years ago.
I never knew when, but I always knew this day would come. It's time for me to talk about the past and to confirm what people have suspected. I used steroids during my playing career and I apologize. I remember trying steroids very briefly in the 1989/1990 off season and then after I was injured in 1993, I used steroids again. I used them on occasion throughout the '90s, including during the 1998 season.
I wish I had never touched steroids. It was foolish and it was a mistake. I truly apologize. Looking back, I wish I had never played during the steroid era.
During the mid-'90s, I went on the DL seven times and missed 228 games over five years. I experienced a lot of injuries, including a ribcage strain, a torn left heel muscle, a stress fracture of the left heel, and a torn right heel muscle. It was definitely a miserable bunch of years and I told myself that steroids could help me recover faster. I thought they would help me heal and prevent injuries, too.
I'm sure people will wonder if I could have hit all those home runs had I never taken steroids. I had good years when I didn't take any and I had bad years when I didn't take any. I had good years when I took steroids and I had bad years when I took steroids. But no matter what, I shouldn't have done it and for that I'm truly sorry.
Baseball is really different now - it's been cleaned up. The commissioner and the players' association implemented testing and they cracked down, and I'm glad they did.
I'm grateful to the Cardinals for bringing me back to baseball. I want to say thank you to Cardinals owner Mr. DeWitt, to my GM, John Mozeliak, and to my manager, Tony La Russa. I can't wait to put the uniform on again and to be back on the field in front of the great fans in Saint Louis. I've always appreciated their support and I intend to earn it again, this time as hitting coach. I'm going to pour myself into this job and do everything I can to help the Cardinals hitters become the best players for years to come.
After all this time, I want to come clean. I was not in a position to do that five years ago in my congressional testimony, but now I feel an obligation to discuss this and to answer questions about it. I'll do that, and then I just want to help my team."
More from CBS Sports.com:
CBS Sports.com: McGwire's career statistics
CBS Sports.com: All-time career HR leaders
CBS Sports.com: All-time Single-season HR leaders