Alexandra was born in Washington D.C., USA, to Mabel Cabot Wentworth, who was First Lady Nancy Reagan's social secretary in the White House, and Eric Wentworth, who was a reporter for the Washington Post. She was a younger sister to Elizabeth "Sissy" Yates.
She was educated at the Dana Hall School for Girls, Bard College, New York University, Columbia University in the USA.
On July 24, 2001 Alexandra appeared on ABC Good Morning America, where she announced her engagement to George Stephanopoulos, a GMA Political Correspondent, after only three months of dating. They were married on 20 November, 2001 and welcomed their first daughter Elliott Anastasia on September 9, 2002.