Send him a letter anonymously. Problem solved.

Since the decision to fire him is already made, and it seems like you're higher up in the company, couldn't you talk to HR and explain the situation and have them inform him of their decision earlier to prevent him future financial trouble for him?

Sadly I know how you feel. I lost a girl because my friend was her assistant manager and he knew she was going to get laid off, but if I told her he'd get fired for breach of confidentiality, she found out that I knew, and basically told me to GFOAD...

Loyalty to a friend or to the corporate machine...

More like FHL, OP

I'm sorry, OP. You can't tell him because it won't do any good to have both of you jobless. Discourage the apartment, maybe by lying and saying you'd like to get a place with him if he can wait a month. Then start a job search for him so when he is canned, you have a listing he can start with.

Maybe say, "Listen there are things I can't tell you, but if you trust me as your friend, don't sign the rental agreement." That is the best way I can see it happening. Even if he asks, just confirm you can't tell him but you are looking out for his best interests.

Keep your mouth SHUT! You can help extend the search process for your colleagues apartment to allow the cut to happen. If you open your mouth, get fired, will your friend pay your mortgage.... HELL NO.

It's actually not illegal to tell him as most of those things employers have you sign aren't constitutional ... So you can tell him , it's your right and his

Show him this FML