The Love Story star is currently embroiled in a legal dispute over a valuable Andy Warhol portrait of Fawcett, which he claims is rightfully his, while officials at a university in Texas allege the actress left the silkscreen picture to them following her death in 2009.
The case has gone to court in Los Angeles, and O'Neal was called to testify on Monday (01Dec13).
During O'Neal's time on the stand at Los Angeles Superior Court, a lawyer representing the University of Texas at Austin questioned him about an incident in 1997 when the actress caught her partner cheating on her with another woman.
When asked about the awkward moment, O'Neal said of Fawcett's reaction, "No (she wasn't angry), she was hurt. She was in shock."
The picture was allegedly hanging above O'Neal's bed when Fawcett walked in on her cheating lover.
O'Neal's testimony became emotional at times, and he came close to breaking down in tears when he was asked to read out a letter which Fawcett wrote to the couple's son, Redmond.