In this Nov. 30, 2018, file photo, U.S. Former First Lady Michelle Obama signs books during an appearance for her book, "Becoming," in New York. U.S. former first lady Michelle Obama turned 55 on Thursday.

Former first lady Michelle Obama reads a book to school children during a surprise appearance at Para Los Niños on Thursday, Nov. 15, 2018, in Los Angeles.

Santa Claus and former first lady Michelle Obama answer questions after Obama read "The Night Before Christmas" to a group of patients at Children's Hospital Colorado in Aurora, Colo., on Thursday, Dec. 13, 2018.

Michelle Obama participates in the International Day of the Girl on NBC's "Today" show at Rockefeller Plaza on Thursday, Oct. 11, 2018, in New York. (Photo: AP)