Tried it. No work. Also, I got that in X/Y, I don't have Omega/Alpha yet. But I know there's an event that is triggered similarily with Diancie in X/Y, so I wonder why's not triggered.
I got it at lv.62, fateful encounter, Pokémon Movie 14. If that says anything.
In case it is hacked, would one of you trade me a legit one? Thanks.
I think the Diancie event in X/Y is only if you got it through the code (Got it through the event npc).
For the event in ORAS you have to get it from an X/Y game.
At least thats what I understand from what I've read in the official statements.
Also, the event in X/Y doesn't do anything, its the one in ORAS that gets you the Mega Stone.