The Sword of the Spirits Series by John Christopher

Luke lives in a society whose finest art is fighting. Since a natural disaster years before, there have been no machines; people must rely on their bodies and wits. All believe in the Spirits- strange, otherworldly beings whose messages are relayed through holy Seers.

Luke has been exiled from Winchester since his half-brother, Peter, came to power. Now Peter's wife has convinced him to permit Luke to return.

In the conclusion to the trilogy set in post-apocalyptic England, Luke returns a triumphant Prince from his expedition in the North, although he loses the three things he cares about most.