Sheryl Crow saw her then partner Lance Armstrong receive a secret blood transfusion and later told investigators what she saw, according to a new book about the doping conspiracy.

Wheelmen: Lance Armstrong, the Tour de France and the Greatest Sports Conspiracy Ever, a new book by Wall Street Journal reporters Reed Albergotti and Vanessa O'Connell, claims that Crow witnessed Armstrong's illicit activities aboard the cyclist's private jet on a trip to Belgium in 2004.

The singer dated the seven-time Tour de France winner after he left his wife Kristin and were briefly engaged but split in 2006.

The book claims:

Rather than try to hide the transfusion from her, Armstrong was completely open about it. He trusted that Crow would have no desire to tell the press or anyone else about the team's doping program. He explained that it was simply part of the sport - that all cyclists were doing the same thing.

Five years after the couple split, Crow was forced to revisit her time with the cyclist when federal investigators launched a criminal probe.

"Wheelmen" claims that Crow informed after Food and Drug Administration criminal investigator Jeff Novitzky gave her an agreement which would protect her as a witness from criminal prosecution.

Armstrong escaped criminal charges when a grand jury dropped the case in 2012 but still faces a string of lawsuits. The Justice Department is suing Armstrong in an effort to retrieve tens of millions of dollars that the US Postal Service paid to the cyclist and his teams.

After years of denial, Armstrong finally confessed to doping at the beginning of this year.