Black Eyed Peas star refused to accept cash from Michael Jackson when the two superstars teamed up to record new material in Ireland in 2006 - because the chance to work with the King of Pop was payment enough.
The hitmaker and producer turned down Jackson's generous offers of flights and accommodation because he didn't want to become one of the many hangers-on who took advantage of the Thriller singer.
The I Gotta Feeling star says, "A week before the trip, he was like, 'My manager is gonna call you to make sure all the travel stuff (is taken care of). Do you fly commercial or private?'
"I was like, 'Don't worry about my flights; I'll pay for my flights... So many people have taken advantage of you in the past... it will be my honour to take myself there and let's just make music to make music. You don't pay for my flight, I won't charge you my fees and if we make good music then the song will make (me) money.'
"He's had a history of people just taking advantage of his success and camping out in the studio and charging him outrageous rates."
And doesn't want to take advantage of his friend now he's not around to OK the release of music the duo worked on in Ireland.
After opposing the release of a posthumous album of Jackson material in the months after the singer's death in 2009, insists only a call from the King of Pop's mum will make him rethink his stance on not releasing the new music.
He tells news show Access Hollywood Live, "When they (record executives) released the last stuff they called me, but no... For me, I've got my moment; my moment working with Mike and seeing Mike and being his friend and because we became friends, I don't wanna be an opportunist.
"If his mum called me and said, 'We gotta do this...' then yes."