1. No one knows it yet, but I found out that the boss is about to quit. I can’t tell you who told me, but let’s just say I heard it though the grapevine.
2. “How did you find out Karen was going to have a baby?” I asked. “I heard it through the grapevine,” answered Julie.

Antonym: straight from the horse’s mouth. The expression suggests that a grapevine, long, tangled and indirect, can act as a means of communication, but the message is not direct and may be distorted or untrue.