Both my friend's

So I'm friends with this couple the female friend (KJ) male friend (TJ) and I know KJ has cheated a couple times cause she's told me about it and just recently TJ found out about one of the times and they fought for awhile but figured it out after a few days. But two days ago TJ text me and asked if I would say he stopped by to see how I was. Shortly after the text KJ calls and asked if TJ was here and I lied and said he had stopped by. I think he was out with another girl should I tell KJ or keep my mouth closed idk what to do!