Bernie Sanders appeared in an ad supporting Hillary Clinton during the 2016 presidential election, according to the new book "Shattered: Inside Hillary Clinton's Doomed Campaign," but he could not bring himself to say the words "I'm With Her" in it.

Authors Jonathan Allen and Amie Parnes reveal in the book that Hillary's team gave Sanders a script for the ad in September.

The script included Clinton's famous slogan, "I'm With Her. Upon seeing the ad and slogan, Sanders said "It's so phony!," according to a report on the exchange from The Hill.

Sanders added that he didn't "want to say that."

According to the book, Bernie still shot the ad without the slogan and did multiple takes addressing different angles such as eliminating support for Libertarian Gary Johnson, but the finished product did not sit well with focus groups and was ultimately cut. Undecided voters were unconvinced of Sanders' support for Clinton in the ad after their bitter fight the Democratic primaries.

The book cites one Clinton aide as saying "People didn't feel that it was an authentic pitch for her and what she wanted to do. It even had some backlash in folks saying that he's not really supporting her."

Sanders endorsed Hillary in July last year, and spoke at a rally for her in Raleigh, North Carolina, in early November when her campaign was suffering due to the lingering effects of an FBI investigation into her use of a private email server.

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