On/through the grapevine
Definition 1 of 1
Pro Tip 1/3Informal Use
This phrase is casual and mostly used in social conversations, not in formal settings. 
I heard on the grapevine that Sandra got engaged.
Pro Tip 2/3Unverified News
Information received through the grapevine may not be reliable as it's passed from person to person. 
Is it true what I heard on the grapevine about the company merger?
Pro Tip 3/3Origin
The phrase originates from the way grapevines spread, symbolizing how gossip travels. 
She got all the updates on the grapevine, just like tendrils reaching out everywhere.