Neil Armstrong lie: 'One small step' quote not spontaneous according to new documentary

A new documentary alleges that Neil Armstrong lied about coming up with his iconic "one small step" line just before stepping on the moon's surface.

Armstrong, the first man on the moon, maintained up until his death that his historic first words on the moon were unplanned.

But a recent interview with his brother Dean claims that he thought up the famous statement months earlier - and that the phrase included a missing "a", according to the Daily Mail.

Armstrong spoke the famous words, "That's one small step for man, one giant leap for mankind."  Armstrong later insisted that he said "a man" but that the "a" wasn't heard because of static.

'If Neil Armstrong says there was an 'a,' then as far as we're concerned, there was 'a,'' NASA spokesman Michael Cabbage said.

Visit NBCNews.com for breaking news , world news , and news about the economy