Robin Williams did not plan his suicide ... in fact, hours before he hanged himself he was making plans for upcoming projects.
A confidante of Robin's who spoke with him the day before his body was discovered tells TMZ ... they had a fairly lengthy discussion about several deals in the works and Robin was "completely engaged in the conversation."
The source says Robin was asking lots of questions about the deals ... inconsistent with someone who planned on killing himself.
The confidante says there was nothing out of the ordinary during the conversation ... saying "He [Robin] was unhappy which he often was, but it was nothing unusual." As for why Robin was unhappy, the source says Robin, like lots of other comedians, "lived in a dark place."
We're also told no one in Robin's life -- including his wife or personal assistant -- had any idea suicide was looming.
We're told the family believes whatever set Robin off on his fatal path occurred shortly before he cut, then hanged himself.