T.R. KNIGHT'S EX: "DA-DA GO BYE-BYE"

GA-GA, GOO-GOO? Baby talk suddenly killed the romance between ex-“Grey’s Anatomy” doc T.R. KNIGHT, 36, and boyfriend MARK CORNELSEN – who, at age 21, is practically a baby himself, and thinks he’s a tad too young for daddy duty.

Trouble began brewing when T.R., diaper-dizzy over the adorable infant girl adopted by co-star/best pal KATHERINE HEIGL, started gushing to his hunky live-in loverboy of two years: LET’S HAVE A BABY!

Mark, swept up in T.R.’s enthusiasm at first, finally told him: LET’S NOT! Then he packed up his toys and moved out.