Khloe's approach -- basically, "thanks but no thanks," Tristan -- comes through loud and clear in the latest episode of "The Kardashians." She was throwing a huge birthday bash for their daughter when Kris pulled Khloe aside to let her know Tristan had paid for the whole party behind her back ... and KK wasn't having it.

Khloe immediately shut down the idea, and was adamant she's paying for the entire baby banger by herself.

She told her momager .. "No, he's not taking care of the whole party."

Kris actually defended Tristan, and insisted Khloe should let him pay -- but after going back and forth, Khloe said, "That's nice, but I won't let that happen."

As you know, their relationship has seen a lot of turmoil before they split.

We broke the story ... they had a baby boy via surrogate, but Khloe later found out Tristan had cheated on her again, and had gotten another woman pregnant -- all behind her back.

In recent episodes of the show, she called TT a "liar." They've since been focused on co-parenting and denied rumors about rekindling.

As for the party, he apparently had a game and couldn't attend, but Khloe still wasn't about to let him pay for the whole party.

In her confessional, she said, "I work really hard to do elaborate things for True and I don't need anyone's help."