Well, if so, he didn’t clue Alan Dean Foster in on this. Foster wrote the first Star Wars spin-off novel* Splinter of the Mind’s Eye, in which Luke has rather romantic feelings towards Leia. This book came out between the first two movies, so it would seem that Lucas hadn’t worked out the whole family relations that early on.
*Foster also wrote the original film’s novelization although George Lucas got the credit on the cover.
