Diddy and Drake -- We Decided to Become Partners ... and We're Gonna Make a Killing

Now we know why Diddy and Drake declared a truce ... they decided peace can be highly profitable for both of them.

We found out the former enemies met at 1:00 AM Monday at Mel's Drive-In in West Hollywood ... just the 2 of them, and of course their bodyguards.

We're told the chat was all about creating a joint venture with both of their names. They kicked around everything from clothing, to jewelry to cigars. They did not zero in on a product line but agreed that it would be mutually beneficial for them to partner.