A Yale University professor slammed ex-Vermont Gov. Howard Dean as a "serious contributor of fake news" after Dean's critical comments focusing on a 2-year-old Halloween costume controversy.

Nicholas Christakis, a professor at Yale University, took to social media earlier this week to call out Dean for being “very misinformed” about the events that took place at Dean's alma mater in October 2015.

“I am sincerely hoping that the explanation for the many falsehoods in your summary of the 2015 Halloween events at our alma mater Yale was not deliberately lying or cravenness by you @GovHowardDean,” Christakis wrote Sunday in a series of tweets.

Christakis was responding to remarks Dean made at a “Civil Discourse and America” panel at Kenyon College in December 2017 which retold some of the events of the Halloween 2015 episode.

In October 2015, Christakis’ wife Erika Christakis came under attack for her response to a request from the Intercultural Affairs Committee that students avoid wearing racially incentive costumes, such as Native American headgear, turbans or blackface.

In an email she wrote to students living in the residence hall where she was an administrator, Erika contended students should be able to wear any costume they want.

“Is there no room anymore for a child or young person to be a little bit obnoxious, a little bit inappropriate or provocative or, yes, offensive?” she wrote. “American universities were once a safe space not only for maturation but also for a certain regressive, or even transgressive, experience; increasingly, it seems, they have become places of censure and prohibition.”

The email sparked instant condemnation throughout the campus, prompting hundreds of students and faculty members to march in protest.

At the time a group of students also confronted Nicholas Christakis on campus. A video of an unnamed student attacking him personally, calling him “disgusting” and a “poor steward of this community,” went viral.

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In his retelling of the episode, Dean appeared to put the blame on the two professors.

“And the wife of the person, the co-leader of this college, wrote another note basically saying, 'Let’s not get too politically correct. Don’t be a snowflake. Do what you want, you should enjoy your ability to dress up on Halloween and let’s stop all this nonsense,'” Dean said. “There was no violence. There was some yelling and some screaming, some people getting very emotional.”

Dean added: “Nobody is attacking the rights of these folks to say political correctness is BS and don’t be a snowflake. But there are consequences to free speech…Being the leader of the college, means you are the students’ advocate. If you then choose to debunk what one group thought was protective, you have lost your purpose to having that job.”

In his tweets, Nicholas Christakis said Dean was “clearly unaware of the breadth of the events during the episode,” before linking to a short documentary about the incident.

He went on to point out several other “falsehoods” before tweeting: “In short, @GovHowardDean, as you can see, you made several defamatory remarks, all grossly untrue. As you say, this is allowable in the USA (and not the UK.) But that should still embarrass you?”

In December 2015, Erika Christakis resigned from her teaching position. Several months later, she and her husband stepped down from their residence hall administrator duties.

“I am very worried that you @GovHowardDean are a serious contributor to the #fakenews problem so afflicting our democracy at present. Please do better? Correct the record that you are falsifying?” Christakis tweeted.

Dean has not publicly commented on the tweets.

Neither Christakis or Dean immediately responded to Fox News’ requests for comment.