The post in question, which has been deleted, called Trump a “pathetic loser” after Republican candidate Roy Moore, who had Trump’s endorsement, lost to Democrat Doug Jones in yesterday’s U.S. Senate special election.

A few hours ago, Cooper tweeted from his account to say that he “just woke up to find out someone gained access to my Twitter account,” with the CNN anchor adding that he had not previously posted anything on Twitter since the weekend.

Earlier in the morning, Cooper’s account posted a reply to a tweet from President Trump in which the president claimed he was “right” to have originally endorsed Republican Luther Strange in the Alabama election for a U.S. Senate seat. Strange lost in the Republican primary to Judge Roy Moore, who was defeated last night by Doug Jones, a Democrat. Trump eventually threw his support behind Moore despite the fact that the former state judge has been accused of sexual misconduct with a minor (Moore denies the allegations).

“Oh really? You endorsed him you tool! Pathetic loser,” the tweet from Cooper’s account said in a reply to Trump’s tweet this morning. The reply from Cooper was later deleted, though some Twitter users captured screenshots of the message.

CNN posted a statement from the Time Warner-owned network’s public relations Twitter account, noting that “someone gained access to the handle @andersoncooper” in order to send the tweet in question. “We’re working with Twitter to secure the account,” CNN said.

https://twitter.com/jenoradio/status/940929025345716224

just woke up to find out someone gained access to my twitter account. i have not sent a tweet in days or replied to any tweets. We are looking into how this happened.

— Anderson Cooper (@andersoncooper) December 13, 2017

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Trump has a long-running feud with CNN, a network that the president regularly refers to as “fake news” due to what he sees as a preponderance of negative coverage. Meanwhile, earlier this year, Cooper actually told CBS late-night host Stephen Colbert that he muted Trump’s account on Twitter in order to avoid seeing the president’s tweets.

UPDATE: A CNN spokesman told Fortune that “geolocation tools” prove the tweet was not sent by Anderson Cooper, who was in Washington, D.C. when the tweet was sent in New York from a phone belonging to the news anchor’s assistant. “His assistant inadvertently left his phone unlocked and unattended at the gym early this morning, and someone took the phone and sent the tweet,” CNN said. “His assistant, who has worked with Anderson for more than a decade, is the only other person with access to Anderson’s Twitter account.”