Interesting discussion in this thread everyone, and I'm sorry I missed out on it first time around 
For my money he discovers about David post-TOS, from a relationship he had pre-TOS. Probably he returns back to Earth following the 5YM and gets bumped up to his desk job, and somehow or other reconnects with Carol, learns about David, maybe they try again on and off but it's not really cohabiting or anything like that (at Carol's request?) which is where David remembers "that overgrown boy scout you used to hang around with". Kirk for his part is increasingly uneasy about being stuck at Starfleet command and yearns space travel again, ultimately the V'ger crisis sees him given the opportunity to do that but it forces the Carol/David situation to a head and Carol asks him to stay away, partially to protect her own heart, partially because she knows Kirk isn't the settling down type and never will be, and partially because she fears the consequences on David.
It is one reason I'm kinda frustrated they flubbed GENS with the whole log cabin/Antonia thing, because it really would have made more sense to use that as an opportunity to explore this period of Kirk's life.
To my mind, learning about David is the one thing that might almost lead Kirk to try retirement. And Carol always feels like Kirk's one real love, like, the one he almost married. Everything fits.
For my money he discovers about David post-TOS, from a relationship he had pre-TOS. Probably he returns back to Earth following the 5YM and gets bumped up to his desk job, and somehow or other reconnects with Carol, learns about David, maybe they try again on and off but it's not really cohabiting or anything like that (at Carol's request?) which is where David remembers "that overgrown boy scout you used to hang around with". Kirk for his part is increasingly uneasy about being stuck at Starfleet command and yearns space travel again, ultimately the V'ger crisis sees him given the opportunity to do that but it forces the Carol/David situation to a head and Carol asks him to stay away, partially to protect her own heart, partially because she knows Kirk isn't the settling down type and never will be, and partially because she fears the consequences on David.
It is one reason I'm kinda frustrated they flubbed GENS with the whole log cabin/Antonia thing, because it really would have made more sense to use that as an opportunity to explore this period of Kirk's life.
To my mind, learning about David is the one thing that might almost lead Kirk to try retirement. And Carol always feels like Kirk's one real love, like, the one he almost married. Everything fits.
