Livestrong spokeswoman Katherine McLane told ABC News Armstrong offered a "sincere and heartfelt apology," which generated lots of tears.
McLane also said he "took responsibility" for the trouble he has caused the foundation, but she did not elaborate regarding whether he admitted he used performance-enhancing drugs while competing, ABC News said.
The move comes days before Oprah Winfrey's interview with the athlete and cancer survivor is to air on television.
Although Armstrong has vehemently denied accusations he used performance-enhancing drugs and was stripped of his seven Tour de France titles as a result of the allegations, sources told ABC News he is expected to finally admit his wrongdoing to Winfrey.
Armstrong stepped down as Livestrong chairman last fall amid the controversy.
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