This question already has an answer here:
I've got 3 princes in my story. Their father the king is STILL ALIVE. Royalty & succession is set up like standard British & European systems. The eldest son (the Crown Prince) went off to war and died in battle. That made the second son the new Crown Prince, but he never married or produced an heir and loved partying so much that he was pushed away from the throne. (If a Crown Prince can abdicate his duties, then that's what he did). The third son has since been named the Crown Prince...and shortly after the coronation is when the eldest brother shows up out of nowhere. It turns out he was kept as a POW and was finally released.
So far they're all princes, dad (the king) is still alive. Nobody has inherited anything, nobody has been crowned the new king. The only change has been who is next in line to BECOME king when dear old dad dies.
The eldest & youngest brothers get along just fine--no conspiring for power or plotting murder! The youngest son has the strongest sense of duty to the crown while eldest brother dreams of a more normal life. The 3rd son hasn't had enough time to get married and produce an heir. I've read so much on royal families and watched every TV show on royal families but I still can't imagine how things might change for the new Crown Prince now that his oldest brother has turned up alive and is able to carry out his royal duties.
Would the eldest son automatically go back to being the Crown Prince? Would the youngest son have to sit tight now that he's officially been declared the Crown Prince?
Would love to hear what you think, along with any examples from history that I've somehow missed!!!