... But a few years later the Danes broke out again into rebellion, and Edward then took in hand their complete subjection.  His chief helper was the great ealdorman Aethelred of western or English Mercia, his brother-in-law.  When this chief died, Edward found his widowed sister Aethelflaed, in whose hands he left the rule of the Mercian counties, no less zealous and able an assistant than her husband had been. (A History of England, Oman, 1900)