BOSTON — A longtime Boston television journalist on Wednesday accused Kevin Spacey of sexually assaulting her 18-year-old son in the summer of 2016 at a Nantucket bar.

At an emotional news conference, Heather Unruh, a former news anchor for WCVB, an ABC affiliate, said that the actor plied her son with “drink after drink” and then reached down his pants and grabbed his genitals. Her son had told Mr. Spacey that he was 21, she said, though he was only 18.

“But,” said Ms. Unruh, regardless of her son’s age, “Kevin Spacey had no right to sexually assault him. There was no consent.” She said she hoped the actor would go to jail.

Mr. Spacey and his spokesman did not immediately reply to email messages seeking comment on Wednesday.