Legal or cheated move?

I was playing with game with a guy which nickname is bern08. I am white and he is black. I just moved my pawn to g4. Then to my surprise, he moved HXG3 and the board now looks like this

Now I still don't know now it is possible? Is it a legal move or a cheated move? Can someone explain for me? Thanks

It's the en passant capture, you should know it in a real game because it is allowed.

Legal.

En passant. Explanation here ... en-passant--cheater2

http://www.chess.com/livechess/game.html?id=183567379

Ok understood. So at least I learn something new. Thank you for your response :-)

Make sure you learn all the special rules:

http://www.chess.com/learn-how-to-play-chess.html#special

They hacked the chess.com servers and made an illegal move.

How did I know this was going to be about en passant when I read the title of the thread?

And why is it that people assume that a chess website would allow illegal moves?

Discussion of cheating is prohibited.

We got the joke already. There's plenty of whiners who can't handle a rule they don't know about and go on a rampage against the whole chess-community. When somebody for once acts like an adult and is actually happy to learn something new, the least we could do is to cut him some slack.

That's very observant of you.

Now that would be an illegal move, unless it's another version.

I feel like I'm missing something here. Another version of what? And not even close to what?

You moved your pawn from g3 to g4, right?  He's definitely cheating.

Yes, you definitely seem to be missing something.

And btw Charles Manson was an adult.

EN PASSANT,  this rule crops up about every two months or so.

En passant

Where's all this hostility coming from? Or Charles Manson? All I did was say that ridiculing someone for not knowing about en passant isn't appropriate forum behaviour (unless they have trouble accepting it as a rule, ofcourse).