http://originaltrilogy.com/forum/topic.cfm/78-interview-with-David-Prowse-spoilers-he-reveals-Vader-is-Lukes-father/topic/12132/darth_ender said:
That article leads me to wonder what bridges exactly did Prowse burn? He claims to have been unaware of the "I am your father" secret until the film's premiere, yet Lucas supposedly cut off most contact after he leaked that secret. I know first instinct here is to accuse Lucas of being paranoid, selfish, egotistical, or whatnot, but does anyone really know why Prowse was cut off? This question probably merits its own thread, but I don't feel like starting one.
http://originaltrilogy.com/forum/topic.cfm/David-Prowse-Banned-Not-Paid-Royalties/topic/11712/
I was going to put the thread title and link it that way but lazy right now.

