Tristan Thompson Reaches Paternity Settlement with Maralee Nichols, $9,500 a Month

Tristan Thompson has hammered out a paternity settlement for his second-youngest child -- where he'll shell out monthly ... TMZ has learned.

Sources with direct knowledge tell us ... Tristan Thompson and Maralee Nichols have agreed to terms for Theo, their 1-year-old son. We're told Tristan will pay $9,500 a month in child support and also covered some of Nichols' lawyer fees.

The $9,500 may seem low considering his NBA contracts have totaled $100M over the span of his career -- but he isn't currently on a team and therefore not earning income, and income is the operative factor in determining child support.

Our sources say Maralee will have sole custody, and while they haven't figured out an official visitation plan yet, those talks will come in the near future.

What's more -- we're told Tristan will be listed as the father on Theo's birth certificate.

Our sources say the paternity settlement agreement will be filed today in L.A. County Superior Court.

Maralee gave birth to Theo in December of last year -- and things got ugly -- Maralee sued Tristan for child support, even claiming he offered to pay her $75,000 to keep quiet about the baby.

It was in January when he came clean after a paternity test, revealing he was Theo's dad, and apologized to Khloe, saying, "You don't deserve the heartache and humiliation I have caused you. You don't deserve the way I have treated you over the years. My actions have certainly not lined up with the way I view you."

While we didn't know it at the time, Khloe and Tristan were expecting a son via surrogate at the time of Tristan's apology -- that baby was born in July.