What we have here strikes me as a Code Geass situation:
An elaborate maneuver of military and political power, and above all else INFORMATION in order for a young disgraced Prince to put himself on the throne.
You'll have to correct my details but I believe I can sum up the broad strokes.
Our story begins with a duel. As it should. Two men vie for control of the city-state Noxus, left in disarray following the last Rune war. It's military regent Boram Darkwill, and his subordinate, Zariv Raedsel. Raedsel insisted on having his men fight him before allowing them to serve under him, killing any man who could not at least wound him. Raedsel was ruthless, cunning and a military genius. But he was no match for Boram Darkwill in personal combat. Then why would such a gifted strategist allow himself to die ignobly and be remembered as a fool whose reach exceeded his grasp.
IT WAS A DIVERSION!
For you see Raedsel had a lover, a woman once named Lilith (see Ryze's Judgement). Lilith held in her possession the magic by which one can receive immortality. Magic spells which allow the caster to absorb the memories, nay the very soul of another into themselves (see LeBlanc's Judgement)...
Fortunately for Raedsel, he had recently participated in a battle which successfully captured the young heir of Demacia Jarvan IV. Using these rituals Raedsel effectively "copied" himself into young Jarvan's mind and allowed him to be rescued by Garen at a critical moment by withdrawing a portion of his forces from the battle, and then days, weeks, or even years later, walks gladly to his death....
Ten years pass. Lilith, foresaking her name and adopting the title of "Le Blanc" constructs a secret society within the magic and political spheres of Noxus known as the "Black Rose". Jarvan IV meanwhile is a broken young man, his features dark and his lust of battle borders on the immoral. Seeking greater and greater prey, he eventually leads a hunting expedition South of the Great Barrier and vanishes...
A short time later, a mysterious and gifted warrior by the name of Jericho Swain begins a meteoric rise through the ranks of the Noxian military with superiors left and right requesting demotion to serve under him. No doubt this is the origin of the "black thorn" military arm of the Black Rose. In English the meaning of "Swain" can be taken as: "country lad", "young lover" or "country gallant" (gallant: chivalrous man). Oh, and ANYONE can fake a limp.
Ten more years pass. Jarvan IV returns to Demacia with great fanfare and immediately begins training a new cadre of soldiers, only accepting those who score a blow against his armour, and requests to join the League of Legends, as does Jericho Swain and LeBlanc. Even with all the knowledge and planning that Lilith had at her disposal there is NO WAY the League could have missed such intense Machiavellian ambitions. Yet all "three" were allowed to compete and no mention of this was said.
Following the Debacle at Kalamanda where Jericho Swain and Jarvan the IV (actually Le Blanc in disguise) nearly started a war, Darkwill was forced to leave the protection of Noxus where his bodyguard discovered their original commander alive and well, and immediately fell upon Darkwill and his retinue, producing additional corpses to prevent further investigation.
Now Swain's right Raven's foot Talon and the Crimson Elite arrive to clean up any "loose ends", eventually leading to Jarvan IV (likely Le Blanc in disguise) bringing two unknown prisoners (likely "Swain" and Katarina Des Coteau) before Jarvan III of Demacia....
As it stands, that likely means that Jericho Swain, interim leader of Noxus, is secretly inhabiting hte body of the heir to the throne of Demacia and is meeting for talks with the King of Demacia behind closed doors with the leaders of the other two principle factions within Noxus.
There you have it folks, Zariv Raedsel has just conquered Demacia and Noxus by feeding!
EDIT: Oh, and the League was complicit with this coup on at least some level. This brings renewed questions about who the mysterious "Reginald Ashram" is or was and how much power Swain truly wields).
EDIT2: I have already found evidence that indicates Swain perpetrated the capture of Jarvan IV. Whether this means Raedsel survived the duel with Darkwill by foresaking his name and title is unknown but Raedsel, Swain, and Jarvan IV are all somehow connected with one another.