Or, how about this; and I know it's possible, because it happened to a friend of mine:
Girl goes to the room. Talks to Kobe, and decides to give him a "Monica" for his troubles. Remember, he just had knee surgery, and could not be too mobile. Now, suppose the girl happened to be skilled in the act; motivating Kobe to pursue other avenues where she was unwilling to go. Now Kobe, after having already shared his DNA with her, assumes that he now has carte-blanche with the girl, and pushes her beyond her limit?
Either way, Kobe is screwed, because if there is DNA, he will either have to claim it was concentual, and lose his wife to decades of Alimony. He cant say there was no sex, if he left his tadpoles on her clothing.