Madonna Jealous of Daughter Lourdes?

Not only does Madonna have to worry about young pop stars crowding her spotlight, she also has to contend with competition from an unlikely source: her 12-year-old daughter, Lourdes Leon!

"I think Madonna can't stand that Lourdes is growing into a beautiful teen," a source tells OK! of the 50-year-old singer. "She seems envious of her youth and looks. She knows Lourdes is going to be gorgeous and will get the attention of the opposite sex. Knowing Madonna's taste for younger guys, it's a matter of course that they'll be dating men the same age. It's disturbing."

Not surprisingly, the superstar is desperately trying to keep her daughter in a permanent state of girlhood. Last year, the beauty team on Madonna's Sticky & Sweet Tour had strict orders not to touch Lourdes's bushy eyebrows.

"That was a battle Madonna eventually gave in to," the source says. "Lourdes recently had them shaped."

Cracks in the once cozy mother-daughter relationship first started to show at a Gucci gala benefiting UNICEF and Malawi last Feb. "Madonna refused to let Lourdes have a hairdresser. She probably didn't want her daughter to look better than her," the source tells OK!.

For the entire scoop on Madonna and Lourdes' rocky relationship, pick up the new OK! — on newsstands everywhere!