Swizz Beatz has a beautiful new wife – Alicia Keys – who just had a bouncing baby boy last week. And now he has a lawsuit to go with his new family.

[READ: Spotted: Alicia Keys Swizz Beatz & Baby Egypt ]

According to TMZ, Swizzy is accused of being a shady business man. The super producer is being sued by a man who claims he wrote Cassidy’s song “My Drink & My Two Step.”

The suit claims Swizz broke him off a lil bit (a very lil bit), while he and Cassidy pocketed the lion’s share of the dough from the hit song.

The songwriter in question — named Antwann Frost — filed the lawsuit two days ago … claiming Swizz hit him up in 2007 to help put together a hit single for rapper Cassidy’s then incomplete album.

According to the docs — obtained by TMZ — Swizz assembled the “drum patterns” and Frost created “all of the other original musical components that shaped and defined” the track that would become a chart-topping hit … spawning remixes by Kanye West, Ne-Yo, and Chingy.

The song was released soon after — at which point, Frost claims, Swizz lowballed him with a $5,000 cash offer and 5% ownership of the song … while Swizz and Cassidy got the bulk share.

Frost rejected the offer … and now dude’s suing for $1,500,000 — claiming he deserves equal partnership in the song with Swizz and Cass. No word yet from Camp Swizz.

VIDEO: My Drink & My 2 Step ~ Cassidy

[Sidebar: Where the hell is Cassidy now?]

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