The pared-down backing track, which has a haunting music-box chime in the background, is still in the demo stage, but even so, the stripped-down new material is in stark contrast to her previous heavily produced pop numbers.
Britney sings:
"Everyday I'm in a daze, looking for that someone "And everyday, I sit and kneel and pray "Oh, sweet love, can I get some? "So why do you desert me, baby boy? "I thought that you were the one"
Then in the middle of the song and Britney is heard on the phone talking to her 'baby boy'. She asks: "Hey baby, what time you gonna get home?"
The lovelorn ballad ends with the lines:
"So why did you desert me, baby boy? "I thought that you, you were the one." "So if you preferred the other one, "She won't bring you the sun."
Spears and Federline, 29, are caught up in an ugly custody battle over sons Sean Preston, two next month, and Jayden James, eleven months.
And yesterday it was revealed she is also being investigated for possible child abuse.
The complaint, lodged with Department of Children and Family Services, alleges poor dental hygiene, as well as poor eating and sleeping habits for the boys.