Khloe Kardashian's boyfriend Tristan Thompson is a dad!

The 25-year-old baller's ex-girlfriend Jordan Craig gave birth via C-section Monday, December 12 and Tristan was there to witness it all, thanks to Khloe.

X17online can now reveal the REAL reason KK brought Tristan back from Cleveland with her, after her latest jaunt to C-town. She paid for them to travel together on a private jet which landed at midnight Sunday morning in LA so he could witness the birth of his first child. The Cavalier center, 25, has Ms. Kardashian wrapped around his little finger, apparently, since he was able to spend the weekend with his lovely lady and have her foot the bill for his five-star, first-class trip to see his baby mama give birth.

A source tells X17online exclusively, "Khloe's really understanding about Tristan's situation -- she's a little embarrassed that her boyfriend is having a baby with someone else, but it happened before she hooked up with Tristan. She wants him to be a responsible dad, but she wants to keep it all on the DL."

So Tristan enjoyed the weekend at Khloe's dining at Kris Jenner's house Sunday night, and hoofed it to Cedars-Sinai Medical Center at 5am yesterday morning to lend some emotional support to Jordy and to be there for the birth of his first child -- a baby boy!

The baby arrived just before noon and only a few hours later, Tristan was at the airport, ready to jump back on another private jet Khloe's paid for, to head home to Ohio. Khloe wasn't at the hospital for the birth - duh - but she met him at the airport to fly back to Cleveland with her him. Way to stand by your man, Khlo!