they don't want you to have that apartment. - dj khaled

Sometimes you just gotta take risks, sometimes you don't, but no matter what, remember it isn't your fault

Quick call the realtor/landlord! Tell him your friend is about to be sacked! He won't want to rent the place and won't have told your friend.

Don't tell your friend directly that he's gonna get fired but tell him not to get the apartment. Tell him it's haunted or something. Last thing you want is you getting sacked for the breach.

What's more important? The right thing or protocol?

Tell him to read FML today.

Friendship first. Tell your friend. If it were you, you'd want him to warn you. You can save him a lot of money and trouble, so don't be selfish, help him out, he will return the favour by keeping the secret.

Business ethics is a difficult thing. I am really sorry OP.

Create a fake email address, mail him the info from a non familiar place like at a coffee shop or something so the isp can't be tracked from the email and tell him. Problem solved.

I don't want to breach confidentiality or anything, so I'll just post it on a popular social media site.