President Trump is already souring on his new chief of staff Mick Mulvaney, who won't serve in his new post until next year.

Mulvaney called Trump a “terrible human being” during a 2016 debate in South Carolina, a tidbit the president was unaware of when he asked the Office of Management chief to take over for chief of staff John Kelly.

“Did you know [Mulvaney] called me ‘a terrible human being’ back during the campaign?” Trump asked an adviser, according to Axios , when he heard about the comment.

The report said Trump was “furious” when he first heard the comment.

A spokesperson for Mulvaney said the remarks were “old news,” and said he changed his mind about Trump after they met for the first time.

Trump said this month that Kelly would be leaving his post by the end of the year. Mulvaney was chosen to be the “acting” chief of staff after Kelly departs, but has not yet taken over the duties of the position.

Many of Trump’s preferred picks for the position withdrew their name from consideration, including Vice President Mike Pence’s chief of staff Nick Ayers.