David Letterman has blasted James Corden as a "tubby kid" ahead of his US chat show debut.
The 36-year-old Brit is to take over 'The Late Late Show' on March 23 - following the departure of previous host Craig Ferguson on December 19 - but the US talk show host has questioned why guest presenters are filling in for the "chubby guy" in the meantime.
Speaking to guest host Regis Philbin on 'The Late Late Show', Letterman quipped: "Did they give you this show? I thought it was that chubby guy that got the show, from Great Britain, from England.
"Let me ask you a question - when they said to you, 'Regis, come to New York and do a show?', did you say, 'Meh, I need four to five months to put my things in order?' No. You were here. You were here Monday, right?
"They call you Friday, you're here Monday. Where's the tubby kid? Who's taking over the show.
"Well, let me ask you this, 'How bad does he want to do a show?' There aren't that many shows. How bad does he want it? Where is he?"
Philbin came to the defence of the Brit, saying: "He wants it, he loves it."
But Letterman hit back: "Really? Well, where is he? Why are we talking to you?
"I'm just saying, if I've invested my money in a guy to do a show and he says, 'I'm going to need a couple of months', I think that's a flag.
"This guy - where is he? Is he even in this country? Don't you think that's a question that should be answered - where is the guy? I do."
However, Letterman eventually admitted he's a fan of the Brit, calling him a "good guy".
He added: "I've met him. He seemed like a very nice fella."