My friend cheated on her bf with another guy but I have the evidence.

So basically, my friend let’s call her Zoe had an affair with her friend Zack, they started dating in jan 2024 and she started the affair with AP in October and I don’t know how long it lasted. The guy she was cheating on her bf with didn’t know she had a bf so he came clean and told one of our friends, he then gave me screenshots of her cheating on Zack. What do I do? Do I tell her bf or keep it a secret?