In an interview with The Denver Post, LeMond said he was happy when he received the subpoena to make a July 30 appearance in federal court in Los Angeles to testify in an investigation of possible fraud and doping charges against Armstrong and his associates.
"The evidence will come from the investigation," LeMond told the newspaper, "and I believe it will be overwhelming."
LeMond also said he believes Floyd Landis was telling the truth in his descriptions of what he claimed was Armstrong's systemic doping program.
Armstrong has denied allegations of doping. On Monday, his attorney sent a letter to the federal prosecutor looking into the case complaining about leaks to the media.
"This appears to be a full-blown and largely unmonitored exploration of Floyd Landis' patently unreliable and routinely changing accusations of possible improper conduct in the professional cycling industry at large," wrote Armstrong's attorney, Tim Herman. A copy of the letter was obtained by The Associated Press.
LeMond, meanwhile, could not discuss what he knows or what he'll testify about at the end of the month, but he said he was looking forward to being part of the investigation.
"I'm hoping it gets as far as it can," LeMond told The Denver Post.
LeMond's belief in Landis' allegations is quite a turnaround from three years ago, when LeMond testified in Landis' doping case. On a remarkable day in that hearing, LeMond told how Landis' manager threatened to reveal then-secret stories of LeMond being sexually abused as a child if he came to the hearing.
"I think there's another side of Floyd that the public hasn't seen," LeMond said that day.
But now, he's a believer in Landis, who recently came clean about his own doping while attacking Armstrong, who has consistently questioned Landis' credibility.
"I think he's telling the truth," LeMond told the newspaper. "I think the level of detail, the descriptions, I think it rings true."