Jackie Kennedy shocked a nation in October 1968 when she added “Onassis” to her famous name.

Aristotle Onassis, a Greek shipping magnate 23 years his bride’s senior, seemed a sudden addition to Jackie’s life, but he and the former first lady had been seeing each other for years. However, it wasn’t just America’s jaw that dropped in response to the wedding. According to Steven M. Gillon’s new book, America’s Reluctant Prince: The Life of John F. Kennedy Jr., Jackie’s children Caroline and John (then 10 and 7, respectively) found out about the nuptials the day before they flew to Onassis’s Greek island, Skorpios, for the ceremony.