Sen. Bernie SandersBernie SandersWarren defends, Buttigieg attacks in debate that shrank the field Five takeaways from the Democratic debate in Ohio New study: Full-scale 'Medicare for All' costs trillion over 10 years MORE's (I-Vt.) campaign manager during his unsuccessful 2016 presidential run says in a new interview that he was shocked by revelations from former interim Democratic National Committee (DNC) Chair Donna Brazile about Hillary ClintonHillary Diane Rodham ClintonWarren defends, Buttigieg attacks in debate that shrank the field Democrats fear Ohio slipping further away in 2020 Poll: Warren leads Biden in Maine by 12 points MORE's control of the DNC.

Jeff Weaver told CNN on Friday that while most Sanders campaign staffers knew the DNC favored Clinton, the extent of the Clinton campaign's control of the party apparatus was unknown.

"It was obviously a shocking revelation," Weaver said on CNN Friday.

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"It was pretty clear that they were on the Clinton side ... I don't think any of us imagined that there was actually a formal arrangement giving the Clinton campaign control of the DNC," he added.

Weaver told CNN that while he has spoken to Sanders about the revelations from Brazile, the two men agreed that reforming the party ahead of the 2020 election is the party's best hope.

Brazile took over the DNC on an interim basis after the Democratic convention last year when former chairwoman Rep. Debbie Wasserman Schultz (D-Fla.) stepped down.

In an excerpt of a forthcoming book published Thursday in Politico, she criticized the financial agreement the DNC had forged with Clinton. 

“The funding arrangement [between Clinton's camp and the DNC] was not illegal, but it sure looked unethical,” Brazile wrote.

“If the fight had been fair, one campaign would not have control of the party before the voters had decided which one they wanted to lead. This was not a criminal act, but as I saw it, it compromised the party’s integrity.”