England’s support for the rival papal faction may have persuaded Pope Alexander II to back William’s invasion, the newly discovered letter from the Vatican archives shows. “In the eyes of Pope Alexander's supporters, it was no longer simply a battle for a crown, but a struggle against those they regarded as followers of Satan,” Dr Licence said. "If Harold had aligned England with Alexander's rivals, it would help explain why the pope was willing to support the overthrow of a crowned king,” Dr Licence said.