Augusta Victoria of Schleswig-Holstein first wife of German Emperor Wilhelm II, King of Prussia died on April 11, 1921. Wilhelm II died June 4, 1941 and had outlived her by a full 20 years.
Empress Maria Alexandrovna, born Princess Marie of Hess and by Rhine was the wife Emperor Alexander II of Russia. She died on June 3, 1880, aged 55. Her husband survived her by 9 months when Emperor Alexander II was assassinated on March 30, 1881.
Holy Roman Emperor Franz II (Emperor Franz I of Austria) out lived his first three wives:
Elisabeth of Württemberg
(m. 1788; died 1790)
Maria Teresa of Naples and Sicily
(m. 1790; died 1807)
Maria Ludovika Beatrix of Modena
(m. 1808; died 1816)
I know that there have been plenty of queens CONSORTS in history whose husbands survived them. Most married queens regnant, however, seem to have become widows -- the most recent examples being Beatrix of the Netherlands, Margrethe II of Denmark, and Elizabeth II of the United Kingdom.
However, there have been exceptions: Isabel I of Castile, Maria II of Portugal, and Juliana of the Netherlands were all outlived by their husbands. Have there been additional examples?