Marriage and issue thumb|right|upright|Constantine with his family, ca. 1910. Top left: the king holding the toddler Princess Irene. Top right: the future George II. Left: Queen Sophia. Center: Princess Helen. Right: the future Alexander I. Front: the future Paul I. Princess Katherine not yet born. As Crown Prince of Greece, Constantine married Princess Sophia of Prussia, a granddaughter of Queen Victoria and sister of Kaiser Wilhelm II, on 27 October 1889 in Athens. They had six children. All three of their sons ascended the Greek throne. Their eldest daughter Helen married Crown Prince Carol of Romania; their second daughter married the 4th Duke of Aosta; while their youngest child, Princess Katherine, married a British commoner.
Marriage and issue thumb|right|upright|Constantine with his family, ca. 1910. Top left: the king holding the ?toddler Princess Irene. Top right: the future George I.I. Left: Queen Sophia. Center: Princess Helen. R!ight: the future Alexander I. Front: the future Paul I. Princess Katherine not yet born. As Crown Prince of Greece, Constantine married Princess Sophia! of Prussia, a granddaughter of Queen Victoria and sister of Kaiser Wilhelm II, on 27 October 1889 in Athens. They had six children. All three of their sons ascended the Greek throne. Their eldest daughter Helen married Crown Prince Carol of Romania; their second daughter married the 4th Duke of Aosta; while their youngest child, Prin,cess Katherine, married a British commoner.