The "Late Show" host had the two stars of "Ben Is Back" booked on back-to-back nights, with Lucas dropping by first on Monday night. So when Julia swung by on Tuesday, Stephen had a little bit of footage he thought she might be interested.
But first, to make sure he might get the best reaction out of her -- and he totally did -- he had to set the stage by asking her about the relationship the two developed before and during the filming of the movie, where Julia does play Lucas' mother.
According to the actress, Lucas spent a lot of time with her and her family, building that bond that would carry through into the film. It went so far that Lucas even spent Thanksgiving of last year with her extended family, which she shared as a very sweet and meaningful memory for her.
"This next thing might be a little rough," Colbert said with a wicked smile after she finished her story. "Because we asked him, Lucas, last night about Thanksgiving."
"Oh no, did you make him say something mean?" she asked.
"I didn't make him say something mean," Stephen emphasized. He then played the clip with no further setup.
In it, Stephen asked Lucas about spending Thanksgiving with Julia, and then slipped in a little question: "Turkey wasn't dry?"
"Little dry," Lucas said, and Stephen caught Julia's expression live as she watched her on-screen son disparage her cooking on national television. It was the kind of jaw drop you can't act. Absolutely priceless.