Judge Arun Subramanian will be an integral part of the Diddy‘s trial — which should kick off in earnest Monday with opening arguments … but, before he became a judge, he was just a civil attorney who really cared about his clients.

We spoke with Mary and Joel Rich — a couple Arun represented in a lawsuit against Fox News after the network ran a story claiming their son leaked thousands of Democratic party emails to Wikileaks in 2016.

After they settled their lawsuit with the network, Mary and Joel say they wanted to take their legal team out to dinner in New York City to thank them for all their hard work … and, Arun immediately agreed to come — with one caveat.

Between 10 and 12 of them went out to dinner at an upscale Italian join in New York City, we’re told … where the wine flowed and the courses kept coming.

The Richs say they don’t know what the bill came out too — but, it no doubt cost Subramanian a pretty penny. Mary and Joel say this is a perfect example of the type of person Judge Subramanian is — respectable, honorable and graceful.

Mary and Joel add Arun treated them like family … always thinking in their best interest — and Mary says she wants to see him again’ cause she wants to give him a big hug.

We’ve spotted Arun on his way to the courthouse multiple times since jury selection in Diddy’s trial began … and, he’s always looked down to earth — headphones on, no indication he’s a federal judge.

Subramanian loves karaoke, buys his own robes online — and is well-respected by his colleagues … the perfect person to handle what is shaping up to be the trial of the year. He’s shown an easy temperament and joking nature in the courtroom which calmed potential jurors all last week.

The judge was born in Pittsburgh — the son of immigrant parents — and, he’s talked about the importance of family. He name-dropped each member of his family in attendance at the Senate Judiciary Committee Hearing For Judicial Nominees in December 2022.

This is arguably the most high-profile case Judge Subramanian has taken on since ascending to the bench … as you know, Diddy is standing trial on five charges — two counts of sex trafficking, two counts of transportation to engage in prostitution and one count of racketeering.