Sorry if this is an exceptionally stupid question. Just fijish4ed the series and it has opened my eyes to this portion of English history
The Last Kingdom, is set during the reign of Alfred of Wessex, at least roughly, starting in the 860s before Alfred's accession to the throne in 871, and reaching as far as the 890s. Æthelred II's reign is almost precisely a century after this, with his ascension to the throne of England upon his half-brother's death in 978.