The 'Wolf of Wall Street' actor, 30, grew up with the Maroon 5 frontman, 35, in Los Angeles and admits he ''always looked up to'' the 'Moves Like Jagger' hitmaker.
He said: ''He's the kind of guy that you never would be [jealous] cause he's not a d**k. He's not a d**k about it, he's so generous and nice to people.
''He's not different now. He's an actual guy...That is a guy who is exactly who he ever was in a great way. And actually, I know a lot of famous people and he's one that has not changed a lid.''
Asked how the duo first met, Jonah told Howard Stern on his radio show: ''Our dads met in the principal's office in junior high. We were in carpool, we lived at each other's houses.''
Jonah also revealed that Adam ''had bad acne when he was growing up,'' and confirmed the singer, who is engaged to 25-year-old model Behati Prinsloo, initially struggled to find a date because he was a ''nerdy.''
He said: ''I always looked up to him, so I don't think I would have had the proper perspective to judge that. I think maybe towards the end because their band got signed when they were seniors in high school and so how could you not be doing well with ladies when you're a guy in a band?''
Jonah's older half-brother, Jordan Feldstein, manages 'The Voice' USA star and his band.
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