I groped my wifes sister

My wife is a twin, her and her sister are almost identical in every aspect except that my wife has had three kids but looks amazing, her sister is unmarried and has had no kids as of yet because she is concentrating on her "Career".
Last night my wife's sister was at our house and i was out in the garage ** around as usual.
I constantly grab and ** my wife "Inappropriately" because i think she is super hot but I came inside and walked to the bedroom and there was who i thought was my wife bent over in just a thong, I walked up and didn't even think about it. I wrapped my arms around her, Grabbed her ** and thrust my hips forward bumping her hips with my **. I knocked her off balance and continued holding her ** helping her get her balance then she spun around and i instantly knew i was **.
her eyes were huge and she said "What the ** are you doing?", I said "Oh my god...I thought you were", totally an unintentional reaction but i looked at her ** and she covered them saying "get out", I left as she slammed the door and was met in the hallway by my wife who said "what's going on". I immediately apologized explaining that i thought it was her and explained what happened, Her sister came out and my wife burst out laughing saying that she was surprised it hadn't happened sooner.
Everyone calmed down and we had a good laugh and i think her sister is cool now but it was tense for a few minutes.
P.S. my wife's sister still has great **. LOL.