William of Tyre
According to William of Tyre, Agnes was eight on her arrival at Constantinople, while Alexios was thirteen. William got Alexios' age wrong (he was born on 14 September 1169) and there is no other source for Agnes' year of birth. If she was in fact eight, she was at least three years too young for marriage, according to most 12th-century views. However, William of Tyre, who was present at the ceremony, seems to describe it as a full wedding ("matrimonii legibus ... copulare"); in this he is followed by some other non-Byzantine sources and by many modern authors.