Britney Spears reportedly shaved her head earlier this year after being warned that traces of drugs could be found in her hair.
Media reports say that ex-husband Kevin Federline told Britney that such a discovery could see him awarded custody of their two infant children in an ongoing custody battle.
"Kevin taunted Britney that even his smoking marijuana near her would leave traces that could be picked up by drug testing," a source told the Daily Mirror.
"He threatened to use that against her in a custody battle.
"After Britney shaved her head, she begged her mum and Kevin to test the hair from the salon but no one claimed it."
The singer, 25, raised serious question marks over her mental state after a troubled period in her personal life by using clippers to shave her head at a California salon this February.
This came a day after Spears admitted herself to a rehabilitation centre.
But a source told the Daily Record that Britney only entered rehab to prove to her family that she was clean.
Reports claim that Federline is seeking sole custody of the estranged couple's two infant boys Sean Preston and Jayden James.
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