What is the literary term for when a character is ignorant of their divine/royal parentage/heritage?Examples would be Oedipus, or King Arthur.
The literary term that you are looking for is known as Anagnorisis. For Arthur, it would be when he was able to pull the sword out of the stone, something that no other person could do, he does it with ease. Since the stone is inscribed with the description of the person who is able of pulling the sword from the stone, it is then that Arthur experiences a startling moment of true revelation.
"Anagnorisis (an ag NOR ih sis) In Greek drama, a startling discovery; moment of epiphany; time of revelation when a character discovers his true identity.
"One of the finest occurs in Sophocles ’Oedipus Rex when a messenger reveals to Oedipus his true birth."
Irony is a contrast between expectation and reality. Irony can create powerful effects, ranging from humor to strong emotions. The following terms refer to three common types of irony.
1. Verbal irony involves a contrast between what is said or written and what is really meant. If you call a baseball player who has just struck out “a hitter,” you are using verbal irony.
2. Situational irony occurs when what happens is very different from what we expected would happen. At a potluck dinner where half of the attendees are vegetarian and are all seated near each other, the plate of roasted ham is placed right in front of them.
3. Dramatic irony occurs when the audience or reader knows something a character does not know. Oedipus Rex is filled with dramatic irony.
In this instance, as a reader we can see the dramatic irony in that we are aware of Oedipus's history. As for Oedipus, it could be situational irony, as he married his mother but he is also her son.