The pair were joking about Ewan McGregor's decision to snub the ITV morning show last week when Susanna noted that she was impressed the comedian had "the guts to turn up".
Adam joked: "Honestly, if I saw I had to sit on a couch with Piers every morning I would say, 'No'. It's only because Susanna is here.
"If this show was called Good Morning Britain with Piers Morgan, you'd never have any guests."
The brunette beauty sighed with relief: "Finally, we have established the real reason. We're no longer living in your world of delusion, Piers."
Susanna Reid praised Adam Hills for turning up to the show
Piers Morgan was not impressed when Adam said he only went on the show because of Susanna
If this show was called Good Morning Britain with Piers Morgan, you'd never have any guests
Changing the conversation to politics, he asked their guest: "What right does an Australian have to come over here and take our jobs and heckle us about our political system?"
But, Adam held his own as he hit back: "As an outsider, you get a different view of what is going on… the best comedians are outsiders. You have John Oliver in America and Trevor Noah in South Africa."
Adam said he wouldn't appear if Piers hosted the show on his own
Good Morning Britain: The best bits
Wed, November 23, 2016
Good Morning Britain: The best bits of the morning TV show with Susanna Reid, Piers Morgan, Ben Shephard and Kate Garraway.
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Good Morning Britain's best bits
Susanna and Piers walked off the show mid-interview with MPs debating Brexit
It came after Piers and Susanna walked off the show half-way through an interview with MPs Iain Duncan Smith and Peter Kyle.
The pair continued to bicker with each other during a Brexit debate and the presenters became so fed up that they stood up and left the conversation.
Susanna jokingly got up to leave the debate but quickly sat back down, however Piers took things one step further and actually left the studio.
Good Morning Britain airs weekdays on ITV at 6am.