The US President made an appearance on 'Between Two Ferns' - a spoof chat show hosted by the actor - and joked the star was put off by the armed security flanking the world leader.
He told 'On Air With Ryan Seacrest': ''Zach actually was pretty nervous.
''It was funny to watch you know, 'cause [of the format of] this whole 'Between Two Ferns' shtick ... His whole character is to go after the guests.
''I think he was looking around seeing all these Secret Service guys with guns and thinking, 'I wonder what happens here if I cross a line?'''
Obama enjoyed his time on the show, and revealed his 15-year-old daughter Malia was impressed at her father sharing screen time with 'The Hangover' star.
He added: ''When I was at the dinner table with the girls, and I said, 'Today I did something with Zach; it's called Two Ferns, I think', Malia was so excited.
''She, you know, had seen all the previous episodes, so I figured it was going to reach our target audience, which was a lot of young people.''
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