In a shocking revelation in the Justin Bieber baby drama saga, Mariah Yeater's ex-boyfriend Robert Powell not only claims Yeater lied about Bieber being the father of her baby, but was paid $50,000 to do so, saying the pair targeted Bieber to make some quick money.

'She just picked him.'

She lied, Powell said flatly in an exclusive jailhouse interview with RumorFix. We were both homeless and living in Oceanside [California] and Mariah was trying to make some quick money.

So Mariah Yeater decided to put her pregnancy to good use, and claim that a celebrity was the father of her toddler-age child, seeling the story to a tabloid for $50,000.

Targeting Justin Bieber, meanwhile, was a combination of convenience and controversy: Yeater recognized his name, and knew that rumors of the underage pop star impregnating a fan would generate big news and even bigger cash.

She just picked him, Powell said. She thought he was famous and all and thought she could get a lot of money by telling the magazine Justin was the father.

She just saw him as an opportunity to make a lot of money, Powell finished.

Powell Real Father: 'She said she was doing it for us.'

Although Yeater claimed she met Justin Bieber at an L.A. concert and had sex in the bathroom, her ex says she never even met Justin, much less slept with him. She'd never even been to his concerts: Mariah Yeater had only seen Justin Bieber on TV.

Speaking to RumorFix from jail, where he is held on burglary, stolen property and drug possession charges, Powell sometimes grew emotional when talking about Bieber and Yeater.

She said she was doing it for us... for our family and son, Powell said. Though the birth certificate doesn't list him as the father, Powell claims to be the true parent of Tristyn Yeater.

She made it seem like it was all for us but she's greedy.

'He's just a little kid, man.'

Despite everything Mariah Yeater has put him through, however, Powell says her still loves his estranged ex, and is willing to forgive her for the Justin Bieber scandal if he can get Tristyn back.

All I want is to be with my son, that's all I care about, Powell said. She can take all her money, I just want my son.

Powell also expressed his sympathy for Justin Bieber, and says he regret having any part in the Mariah Yeater baby daddy scheme.

He's just a little kid, man, Powell said. He don't need to be going through all this drama. He got a career and sh*t to focus on. I feel sorry for the dude.

Mariah's attorneys have said Powell's accusations are all wrong, but have no further comment.