ITV presenter Julie Etchingham wrote on Twitter: "So sad to learn this - we have worked on many big stories together & Al is a trusted friend and guide to many of us."

The reasons for the veteran broadcaster's departure have not been confirmed, but it came weeks after he was involved in a Twitter exchange with a black man in which he quoted a Shakespeare passage including the phrase "angry ape".

Stewart has used this verse once before on Twitter in response to a user who was not identifiably black.

After posting a photo of herself in the news studio with Stewart, Singh told Good Morning Britain: "I texted him last night to see if he was OK, he said he was OK. I feel really upset about it."

Stewart would "pore over every word" when he was writing the news headlines, she said.

'He did not think it was a slur'

"He understands the emphasis and I think perhaps he might be thinking, gosh, maybe I should have re-read that quote and thought about it twice," she said.

"In my gut, I would put my house on it that not for one second did he write that quote thinking that it was in any way a slur on anyone's skin colour."

According to reports and screengrabs, Stewart engaged in a row about how the monarchy was funded, and posted a passage from Measure For Measure that included the line: "Most ignorant of what he's most assur'd - His glassy elegance - like an angry ape."

At the time, the user - who has received online abuse since Stewart's departure - responded: "Just an @ITV newsreader referring to me as an ape with the cover of Shakespeare. Measure for measure, Alistair [sic] is a disgrace."

'Extraordinarily generous'

Singh added that Stewart had "only ever been gracious and encouraging to me" and had supported black talent in the newsroom.

While she did not know what the exchange was about or what Shakespeare's original meaning was, she added: "Do you go back and unpick the whole of literature? My God, you know, it wasn't a quote from Enoch Powell."

Good Morning Britain host Ben Shephard said on the programme: "I've been lucky enough to work with Alastair over the years as well, and he's an extraordinarily generous person with experience as a broadcaster to work with."

ITV News arts editor Nina Nannar and GMB chief correspondent Richard Gaisford were among the other colleagues to post warm words about Stewart's character and career.