Pop singer Lady Gaga has hit back at the lawsuit filed by her former mentor, insisting the business agreement between them was 'unlawful'.

Contactmusic.com reports that producer Rob Fusari has filed a $35 million lawsuit against her alleging that she dumped him as soon as she became a star. He produced several tracks on Gaga's debut album, 'The Fame', including the hit 'Paparazzi'.

According to the legal papers, Gaga and Fusari created a joint company called Team Love Child LLC, of which Fusari had a 20 percent share.

Gaga's lawyer, Charles Ortner, has responded to the lawsuit in a letter, claiming the pair's arrangement was 'structured in such a way as to mask its true purpose - to provide to the defendants unlawful compensation for their services as unlicensed employment agents.'

Ortner also claims Fusari and his company charged Gaga 'an unlawful fee for their purported services,' reports contactmusic.com.

But Fusari's legal representative Robert S. Meloni has hit back at the claims calling them 'ludicrous'.

'Fusari is a partner in the Team Love LLC with Gaga and her father (through their company Mermaid). Rob was no more of an 'agent' for her than she is a Roman Catholic nun,' he said.