Can I find out if my Beldum Shiny is legit?

Picked up a copy of Omega Ruby the other day and as soon as I started it up I noticed a section saying "mystery gift" or something like that. I connected to the internet and got s a shiny beldum, it says it was met at a fateful encounter which I know from past experience means it could be a hacked mon. I can give more details on him if anyone thinks they can tell if it's hacked or not.

Also, I started up my copy of Y and tried to do the same thing but it just says "no gift found" my copy of Y was second hand though and i wiped the cart after buying it, i don't know if that effects it or not.

Omega Ruby & Alpha Sapphire had a Shiny Beldum as a Mystery Gift giveaway via WiFi from the release of the games until the 15th of January. Since the 15th was just 3 days ago, I'm thinking that this was the one you picked up via Mystery Gift.

If it had a Metagrossinite as its held item, then it's the real deal.

That whole Fateful Encounter thing is in there because it gets used with Pokemon that are event Pokemon like the Shiny Beldum with the Metagrossinite.

In the future, you can post questions like these in the Quick Questions threads in the respective game's section instead. Example for ORAS: http://www.pokecommunity.com/showthread.php?t=338987

Your question was still answered, so I'll just lock this thread now. If you have any further similar questions, refer to the QQ threads!