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Usher's custody battle with his ex-wife has turned nastier after he suggested delaying the next hearing to allow both parties to recover from the death of his stepson.

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Tameka Foster's 11-year-old son, Kile, died last month from injuries sustained in a personal watercraft accident, and the R&B singer asked for a break in the custody battle so as not to cause "unnecessary stress and strain" to either himself or his ex.

But Foster insists the singer's sympathy comes with an agenda, and in new court documents, obtained by TMZ, she claims his concerns are "bogus."

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She reports Usher visited her son once during his 15 days on life support, and he refused her request to tweet a message urging fans to pray for Kile -- instead posting a photo of his own breakfast.

In her documents, Foster insists Usher's attempt to postpone the next custody hearing is "simply a transparent sham" and she has asked the judge to deny his request.

The next hearing is scheduled for Aug. 13.

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