the way i see it, there's 2 choices, unless you divulge further i cant really comment much more.

1 - if said person is in danger, be it personal or otherwise, then you have an obligation to tell them.

2 - if it is a long going fued, or divorce etc. then stay well clear and act like you have never heard or seen anything.

other than that, i dont think there is much more i can say.

good luck