Thomas Becket, who was once friends with King Henry II, became Archbishop of Canterbury in 1161. Tensions grew between them as Becket took his religious duties seriously while Henry wanted to assert more control over the church. This culminated in Becket fleeing England after disagreeing with Henry's Constitutions of Clarendon. Though they reconciled briefly, Becket excommunicated bishops allied with Henry upon his return, angering the king. Four knights heard Henry say he wished to be "rid of this troublesome priest" and murdered Becket in Canterbury Cathedral on December 29, 1164. Historians have debated whether Becket or Henry was ultimately responsible.