Sydney-based insurance agency executive Andrew Gibson, 43, admits his father was stunned when he told the truth about his sexuality - but actor Mel was always supportive.
Andrew tells the Globe, "When I told my dad, he cried and blamed himself... That broke my heart.
"Mel just said, 'It's not my choice, but I love you and you're my brother.'"
Andrew has been standing up for his older brother in recent years as the Hollywood star's reputation took a hammering following an anti-Semitic outburst at a cop during a DUI arrest and the breakdown of his tempestuous romance with Russian singer Oksana Grigorieva.
Andrew reveals he was shocked by the news reports detailing his brother's DUI arrest in 2006, recalling, "When I heard them, I just thought, 'That isn't Mel. He has never said anything abusive, aggressive or racist in his life'."
Gibson's younger brother also admits he is still upset that his sibling is no longer married to longtime wife Robyn - the mother of his seven kids - insisting she was "the most important thing in that family," and adding, "She held it together... looked after Mel."