Trump supporters stormed the Capitol building on Wednesday with a violent riot that killed four in scenes Morgan described as "utterly horrific".
The president posted a video to the rioters on his Twitter account telling them "I love you", in a message which contributed to a suspension from the social network for “repeated and severe violations” of its Civic Integrity policy.
Read more: James Corden brands Donald Trump a ‘lunatic’
Writing for MailOnline on Thursday, Morgan said: "I can't remain friends with someone who says he 'loves' a bunch of violent Nazi sympathisers and white supremacists who've just launched a deadly attack on the epicentre of US democracy itself and thinks they're 'special people'."
The 55-year-old also claimed to have got in touch with a senior aide to Trump to instruct them to "tell him to get on TV now, admit defeat and call off this outrageous coup".
The Good Morning Britain presenter has frequently referred to Trump, whom he met after a stint on Celebrity Apprentice in 2008, as a “friend”.
He interviewed Trump on GMB prior to his election to office in March 2016 and again in 2018.
The pair appeared to fall out last year when Morgan branded Trump "reckless" for his response to the coronavirus pandemic, prompting the president to unfollow him on Twitter.
However, Morgan said they last spoke just ahead of the US election in November.
Morgan added: "In the past year, he has morphed into a monster that I no longer recognise as someone I considered to be a friend and thought I knew."
He described the Trump's "antics" since losing the election to Joe Biden in November as "utterly contemptible".
Watch: Electoral College votes certified
“I never imagined he would be capable of becoming what he's now become – the deranged figurehead of a bunch of hard-right conspiracy-theory-fuelled fanatics intent on destroying American democracy,” he said.
Morgan also stated that Trump should not be allowed to hold the office of president for any longer, two week ahead of Biden being sworn-in.
On Thursday, the final electoral count which had been disrupted by Trump’s supporters was finally able to be concluded, with Congress confirming Biden’s win.
Watch: Lawmakers call for Trump’s removal from office