post apocalyptic fantasy trilogy

This is a trilogy of books that takes place in a post apocalyptic world. The main protagonist is a teenage boy in the first book, and he is chosen to be the future king by the religious leaders of the main faith called Spiritists (?). There are Christians, but they are the minority. People that are born with deformities (from the radiation fall out of years ago) are called polymuffs, and are treated as servants/serfs. Any animal that is found deformed is killed.

Technology of any kind is forbidden, and is secretly being used by the Spiritist leaders underground. The boy grows up and does become the leader. He goes north and visits another kingdom and that is more tolerant of people with deformities. He falls in love with a girl named Blodwen(?) who is the daughter of that king of the northern country. She falls in love with his friend, and a war is about to ensue, and but is stopped by one of his other friends.

Technology is slowly being rediscovered in the nothern country where the main character stays, and his love interest marries his friend.

The cover of the last book in the trilogy had the main character standing on cliff edge overlooking a battle field(?) and he was holding a something that looked like a machine gun.

This might be the The Sword of the Spirits trilogy. It's many years since I read it, but it rings a bell and apparently there's a Blodwen.

Yes, that's it! Thank you so much!

Aka the "Prince In Waiting" trilogy. It's by John Christopher.