Is This Chess Position Illegal? #2

Last puzzle, you guys were able to spot the mistake quite quickly, and even though it had a small flaw, it was not exactly realistic. But nonetheless, I made a mistake, so I have come back with a newer, more difficult challenge! I have now perfected my next puzzle (below) and made absolutely sure it is exactly what I wanted.

"I find it quite fun to search a chess board to see if a certain position is legal or not. And by legal, I mean it is a something you can find in a normal game. Is this position able to happen in an actual game? In other words, is this position legal or illegal? Post your answer, and tell me what you think the answer is. If illegal, also tell me what is wrong with the position. I'll post the solution when someone answers correctly."