Carlson was fired from the news channel in April, and he insulted his ex-co-worker on Wednesday night while criticising the mainstream media with the former US president in a discussion streamed on X, the platform formerly known as Twitter.
Carlson spoke to Trump instead of covering the GOP debate, providing an alternative viewing option to the Fox News presidential campaign coverage.
When the pair began discussing Joe Biden, Mr Trump said: “I don’t think he’s capable of doing anything” and alluded to someone else being in control of his actions.
Referencing the 2020 presidential election, Mr Trump said: “Look, when I debated him, I said, how come? And this was in front of probably not a friend of yours, Chris Wallace. He was the moderator.”
After Carlson agreed that Wallace is “not a friend” of his, Mr Trump replied: “He wants to be Mike, but he doesn’t have the talent? It’s one of those,” Mr Trump continued.
Attacking his former colleague, Carlson then retorted: “B****y little man.”
Mr Trump then joined in with an insult, claiming Wallace “wanted to be his father, but he didn’t have the talent of his. His father was great.”
“Little fussy man,” Carlson interjected, criticising Wallace once more.
“His father interviewed me in 60 Minutes. It was actually a 10. Can you believe it,” Trump said.
“His father had a talent at least,” Carlson replied with a laugh.