Does She Need To Ask Permission To Date Her Friends Ex-Boyfriend?

We love getting emails from listeners who need help and this one is very interesting -

Dear Rik, Michele and Cefus -

I recently ran into my friend's ex-boyfriend. I always thought he was attractive. Do I need to call her before asking him to my office Christmas party? I haven't spoken to my friend since 2013. Does the 'Golden Rule' of 'not dating someone your friend dated' apply?

Thanks,
A.S.

Should she notify her friend or just ask the guy out?