Dana Tran -- the mother of one of Sean "Diddy" Combs' children -- is casually dating Desmond Scott ... TMZ has learned.

Sources familiar with the situation tell TMZ ... Dana and Desmond have been spending time together since Desmond's estranged wife, Kristy Scott, filed for divorce.

We're told things between Dana and Desmond are not particularly serious ... at least not yet.

In fact, our sources say Dana and Desmond have only been seeing each other recently ... and that's kinda significant.

We broke the story ... Kristy filed to divorce Desmond back in January ... and she cited infidelity as the reason for the split.

A couple days after the divorce filing, we saw Desmond making out with model Marissa Springer in a Houston club.

Now, he's dating Dana ... and our sources are adamant there was no overlap between Desmond and Dana's relationship and his marriage.

Meanwhile, Diddy is locked up in New Jersey serving out his federal sentence for a couple prostitution convictions.