Los Angeles: Estranged Hollywood couple Angelina Jolie and Brad Pitt may lose custody of their adopted children Maddox, 15, and Pax, 13.

Jolie and Pitt, who are currently battling for custody of their six children, will reportedly have to send back Maddox and Pax to their biological parents, reports radaronline.com.

The biological mother of Pax, who was adopted by Jolie and Pitt from a Vietnam orphanage in 2007, will soon be released from a prison in Vietnam and wants to reunite with her son, radaronline.com reported, citing a source.

"I'm sure both Brad and Angie are freaking out over this. It's been a fear from day one that the biological parents of their adopted kids would resurface," the source said.

While Maddox's Cambodian parents are believed to have passed away, radaronline.com claims that his adoption was "brokered by a crooked agent" named Lauryn Galindo, who was later jailed for visa fraud and money laundering involving more than 800 adoptions. 

Children's rights groups investigating Galindo believed Maddox's destitute mother sold her son for $100. 

"The situation with Pax, and the increased fear over Maddox, is terrifying to Brad and Angie," the source said.