He was a true apostle - or so I've always been taught - until he despaired of salvation.
So, yes, technically: thirteen. It's odd to hear, but it's true.
Ahhh, biut Judas never received the mark of the blood of the lamb, having stormed out before the seder was complete. :^)
Seriously, there were only 12 apostles plus one Messiah bringing the total to 13. Judas was one of the 12.