US President Donald Trump is publicly feuding with the husband of one of his closest advisors.
For months, George Conway - spouse of White House counsellor Kellyanne Conway - has been taking shots at Trump on the President's own favourite social network, Twitter.
Trump largely ignored him until this week, when George Conway questioned his mental state, suggesting the President was showing "signs of serious mental instability" and shouldn't have "command over the world's second-largest arsenal of nuclear weapons".
In response, Trump said George Conway was "VERY jealous of his wife's success and angry that I, with her help, didn't give him the job he so desperately wanted".
"I barely know him but just take a look, a stone cold LOSER & husband from hell!"
In a separate tweet, Trump called his employee's husband a "total loser".
Rather than ask him to back off, Kellyanne Conway - who coined the infamous phrase 'alternative facts' in attempt to justify false information being spread by the White House - defended her boss.
"He left it alone for months out of respect for me," she told US news site Politico. "But you think he shouldn't respond when somebody, a non-medical professional accuses him of having a mental disorder? You think he should just take that sitting down?"
George Conway - who was actually offered high-ranking positions in the Trump administration, but reportedly turned them down - fired back in a series of tweets.
"Congratulations! You just guaranteed that millions of more people are going to learn about narcissistic personality disorder and malignant narcissism! Great job," he said directly to the President.
In other tweets, he joked about Trump's legal problems.
Prior to the becoming President, Trump had actually praised George Conway - who used to live in Trump World Tower in Manhattan - for "assistance in ridding Trump World Tower of some very bad people" and his "truly great voice", according to a letter obtained by news site Vox.