Piers Morgan revealed on Life Stories that the actor declined to make an appearance.
The Gavin & Stacey pair became best friends for a time, but parted ways after their BBC Three sketch show and movie Lesbian Vampire Killers were panned by critics.
Morgan told Corden: "We asked him to take part in this programme, and he chose not to."
Corden, appearing slightly shaken, responded: "I didn't know that," before adding, "But I can understand why.
"Because it's a hard time to talk about. And I still hope one day we can do something together, again. It won't be a TV show or a sketch show."
Piers Morgan's Life Stories: James Corden Uncut airs tomorrow night at 9pm on ITV2.
> Corden: 'Sketch show was a mistake'
> James Corden plans 'break' from Horne
Watch a clip of BBC Three sketch show Horne and Corden (2009) below: