Charlemagne threatened to avenge an assassinated king

In 796, King Æthelred of Northumbria was assassinated, provoking the black anger of Charlemagne who held him in high esteem. The Frankish sovereign described the inhabitants of this region as a treacherous and perverse people before threatening to avenge this murder. His ambassadors present on site received the order to return to Northumbria to recover the gifts initially offered to the court.