From Harpers Bazaar:
Years before Aristotle Onassis married Jacqueline Kennedy on October 20, 1968, he was involved with her younger sister, Lee Radziwill.
Radziwill, a former public relations executive, became close with Onassis at the end of her second marriage to Prince Stanislaw Radziwill, while her sister was still in the White House. According to Vanity Fair, Larry King asked Lee if she ever considered marrying Onassis, to which she answered, “Who didn’t?”