Judgement Kayle???

So I just found out that Judgement Kayle is rare, and I have no idea how I got it. I thought I got it on sale a while ago, but that doesn't seem to be the case lol. A friend told me that I had to participate in a tournament to get it, but I don't even know what that is XD. I've also heard that you got it as a reward for playing in Season 1 but if I remember correctly I made my account around when Orianna and Vayne came out and I think that was Season 3.