What is the lore behind Jarvan IV and Jericho Swain?

Question

In Jarvan IV's Relations, it said this quote.

Jarvan IV is the arch-enemy of Jericho Swain.

I looked at their lore.

And didn't find any information about this relationship.

Why they are arch-enemies? When did this occur?

Answer 1

Try reading the first paragraph of Jarvan's lore again; I'll quote the relevant section:

In his most crushing defeat, he was outmaneuvered and captured by a Noxian battalion under the command of Jericho Swain. This mistake nearly cost him his life at the hands of Urgot, but he was rescued by the Dauntless Vanguard, an elite Demacian strike force led by Jarvan’s childhood companion, Garen.

Jarvan hates Swain because Swain captured him and nearly had Jarvan executed.

Additionally, Swain hates Jarvan because Noxus hates Demacia, and the two are each prominent leaders of their respective city-states.

If someone tried to have you executed after embarrassing you and slaughtering all your men, wouldn't you hold a grudge? ;)

Answer 2

From Swain's League Judgement:

Jarvan was no longer the thirteen-year old child prince that Swain had been sent to dispatch.

From Jarvan's League Judgement:

“What do you think you’re doing, Swain? This is a hallowed place. Your treacherous games will not be tolerated here.”

Not to mention all the fighting over Kalamanda, which can be read about in the Journal of Justice, especially issues 11, 18, 20, 21, 23, 24, 25, 27, and 29. In issue 25, Jarvan and Swain get into a fist-fight as war seems inevitable.

The entire feud is never explained, but hinted at in multiple places. There's plenty of rumors that run wild on the forums!