There's been a lot of big lawsuits floating around lately.

But none bigger than the one Akon's former business partner just hit the rapper/singer with.

Devyne Stephens helped launched Akon's career and says he's entitled to 40% of what Akon's earned since 2006, including record sales, touring rights, royalties and more.

Stephens concedes they've argued about the exact terms of their contract in the past. But in his legal filings he says they worked that all out in 2015, and decided upon the 40 percent.

But since then Stephens hasn't seen a dime.

So he's suing for $150 million, the amount he says he owed. Which means Akon has made about $400 million over the past 11 years.

Not bad at all.