Michael Douglas was horrified when his son was subjected to anti-Semitic abuse.
The 'Wall Street' actor had a "not pleasant" discussion with a man who left 14-year-old Dylan - his eldest child with wife Catherine Zeta-Jones - in tears following a tirade sparked by the teenager's Star of David necklace, a symbol of his Jewish faith.
Michael - whose father Kirk is Jewish but mother Diana isn't - said: "Last summer our family went to Southern Europe on holiday. During our stay at a hotel, our son Dylan went to the swimming pool. A short time later he came running back to the room, upset. A man at the pool had started hurling insults at him.
"My first instinct was to ask, 'Were you misbehaving?' 'No', Dylan told me through his tears.
"I stared at him. And suddenly I had an awful realisation of what might have caused the man's outrage: Dylan was wearing a Star of David.
"After calming him down, I went to the pool and asked the attendants to point out the man who had yelled at him. We talked. It was not a pleasant discussion. Afterward, I sat down with my son and said: "Dylan, you just had your first taste of anti-Semitism."
The 70-year-old actor - who also has daughter Carys, 11, with Catherine and grown-up son Cameron with ex-wife Diandra - wants people to work together to tackle anti-Semitism in the hope of eradicating it completely.
Writing for the Los Angeles Times newspaper, he added: "If we confront anti-Semitism whenever we see it, if we combat it individually and as a society, and use whatever platform we have to denounce it, we can stop the spread of this madness.
"My son is strong. He is fortunate to live in a country where anti-Semitism is rare. But now he too has learned of the dangers that he as a Jew must face. It's a lesson that I wish I didn't have to teach him, a lesson I hope he will never have to teach his children."