In 868, Alfred married Ealhswith, daughter of a Mercian nobleman, Æthelred Mucil, Ealdorman of the Gaini. The Gaini were probably one of the tribal groups of the Mercians. Ealhswith's mother, Eadburh, was a member of the Mercian royal family.
They had five or six children together, including Edward the Elder, who succeeded his father as king, Æthelflæd, who became Lady (ruler) of the Mercians in her own right, and Ælfthryth who married Baldwin II the Count of Flanders. His mother was Osburga daughter of Oslac of the Isle of Wight, Chief Butler of England. Asser, in his Vita Ælfredi asserts that this shows his lineage from the Jutes of the Isle of Wight. This is unlikely as Bede tells us that they were all slaughtered by the Saxons under Cædwalla. In 2008 the skeleton of Queen Eadgyth, granddaughter of Alfred the Great was found in Magdeburg Cathedral in Germany. It was confirmed in 2010 that these remains belong to her — one of the earliest members of the English royal family.
Osferth was described as a relative in King Alfred's will and he attested charters in a high position until 934. A charter of King Edward's reign described him as the king's brother, "mistakenly" according to Keynes and Lapidge, but in the view of Janet Nelson, he probably was an illegitimate son of King Alfred