"Going to" expresses the future, and generally some sort of plan (e.g "I am going to visit my mother") or, as this case, prediction or destiny (e.g. "Trump is going to lose the election"). We don't yet know the result, because we are talking about the future relative to now. But it need not be relative to now; it can be relative to any time point. So if you say "was going to", that means it is in the future relative to that time in the past, and in the rest of the sentence you can determine whether it has in fact turned out that way. Your sentence implies that the dream did indeed materialise.

When someone uses, ¨ never knew this would happen¨ it refers to all of the time prior to the event actually taking place. So if you were to say, ´ I never knew that I would be writing this on August 15, 2016.¨ That would mean that you had no idea that you would write this on August 14th, 13th, 12th, 11th, 10th.....

Could you provide the sentence that comes before this sentence?