People.com said Monday Vanderbilt, 87, talked about Carter's death on the new syndicated talk show of her surviving son Anderson Cooper.
During their conversation, Vanderbilt recalled how Carter leaped from the 14th-floor terrace of his family's New York penthouse apartment.
"When he went … I thought he was going to come back, but he didn't," People.com quoted Vanderbilt as saying in the interview. "He let go, and there was a moment when I thought I was going to jump over after him.
"I thought of you and it stopped me from [jumping]," Vanderbilt told Cooper. "You never get over it, but you learn to live with it."