First of all, please, start calling her a ****. One of the guys wrote absolutely correct, if she slept with you, you must have other chachas, mamas, her old class mates, friends etc. who also ****ed her.
If you have any dignity, first and foremost, do a DNA test and find out is it you or someone else's child. Then either ways, confront your brother, tell him the truth, he might forgive you but definitely divorce her.
Different personality, definitely your and you brother's personalities are different. I don't think anyone (EXCEPT A DOG) can or will do what you did. I don't think that the child will have your character, cause you don't have any.
Shame less SOB
IF YOU HAVE ANY SHRED OF DIGNITY, TELL YOUR BROTHER, KICK YOURSELF AND THAT WHORE OUT OF THE HOUSE AND HOPE ALL GOES WELL.
"cause WHAT GOES AROUND, COMES AROUND. WAIT AND WATCH, SOMEONE WILL END UP ****ING YOUR WIFE AND GETTING her PREGNANT AND IN A MORE OBVIOUS WAY.
YOUR WIFE WILL PROBABLY GET PREGNANT IN HER ***... How about that shrap for you **** head!