Stanhope, 49, has written an op-ed for The Wrap that Depp, 52, told him his wife of 15 months threatened to blackmail him as their marriage fell apart.
On May 21, hours before Heard claimed that the "Pirates of the Caribbean" star hit her with a cell phone during a violent argument, Stanhope and another friend named Bingo spent most of the day at the couple's LA home.
"We assumed initially that his dour mood was because of his mother's death the day before," the stand-up comedian writes.
Heard, 30, filed for divorce two days after her alleged fight with Depp, and on May 27 she was temporarily granted a restraining order against him, after submitting a deposition in which she claimed she was "extremely afraid" for her safety.
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The friends left Depp to get some rest, but later that night police were called to his house for a domestic dispute.
Police, however, has said that despite Heard's claims, they found no evidence for a report when they were called to the home.
"Everything Johnny had told us that she'd been threatening had actually come to be," Stanhope writes. "It blew up in the news, raced through the Internet like a plague and blew up on Twitter... People are swarming with torches on social media."
"Abusing women is bad," Stanhope adds. "Johnny doesn't abuse anyone. And he told me that day ahead of time that she'd pull something like this. Johnny Depp got used, manipulated, set up and made to look bad. And he saw it coming and didn't or couldn't do anything to stop it.