A new documentary has cast doubt on Neil Armstrong's claims that he came up with his iconic 'one small step' line hours after touching down on the surface of the moon.

The first man on the moon had stubbornly maintained up until his death in September that his historic words were unplanned, but a recent interview with his brother claims that he thought up the famous speech months before the July 1969, Apollo mission - and that the phrase he planned to utter did include an 'a'.

Hundreds of millions around the world heard the NASA astronaut say, 'That's one small step for man, one giant leap for mankind', but Armstrong insisted that he said 'a man' but that the 'a' was not heard because of static.

In a rare interview three months after the NASA pioneers death, his brother, Dean, recalled that Neil showed him a written version of the speech months before the Apollo 11 launch, clearly stating, 'that's one small step for a man, one giant leap for mankind.'...