Usher has left 'The Voice' to look after his children.

The 34-year-old singer - who secured full custody of his sons, Usher V, five, and Naviyd, four, after a lengthy battle with his ex-wife Tamika Foster - allegedly no longer trusts anyone else with his kids after their former nanny, Cecilia Duncan, filed a lawsuit against him, claiming she was unfairly fired for asking for overtime pay.

A source said: ''He's at the point where he doesn't trust anyone to take care of his boys. Besides, he didn't fight so hard for custody just to hand them over to a nanny.''

His fellow judges Blake Shelton and Adam Levine have tried to convince him to stay on the show, insisting that celebrities are always in the firing line for people who use stars for their stack of cash.

Speaking to the National Enquirer, an inside source said: ''Blake told him that stars are always targets for people who think they can treat celebrities like cash registers. But Usher is really steamed about this lawsuit. He believes he's always been generous to people who work for him.

''If he has to leave 'The Voice' to free up more time to be with his kids, he's ready to do it.''