When Neil Armstrong became the first man to walk on the moon on July 20, 1969, his broadcast declaration, “that’s one small step for man, one giant leap for mankind,” became practically synonymous with his name.

Before the landing, Armstrong had been flooded with suggestions of lines he might use for the occasion. As biographer Andrew Chaikin writes in “A Man on the Moon,” several people suggested quoting Shakespeare or bible passages. Armstrong ultimately rejected all of those in favor of his own creation, a line he consistently claimed was thought up on the spot.

Armstrong also later said that the quote had gotten bungled by transmission static, that he had really said “that’s one small step for a man,” but that the “a” had mysteriously been left out when it was broadcast back on earth.

The confusion over his precise wording led to years of speculation about whether the astronaut had simply forgotten to say it, perhaps falsely blaming it on the transmission. But in the new BBC documentary, “Neil Armstrong — First Man on the Moon," members of Armstrong’s family – who up until now had been relatively tight-lipped – have finally addressed the famous the line, and their version of events doesn’t entirely match up with Armstrong’s.

In an interview for the movie, Dean Armstrong claimed that his brother Neil had decided on the famous line months before the moon landing, passing him a piece of paper with the words written on it while the two were playing a board game.

“Before he went to the Cape, he invited me down to spend a little time with him. He said 'why don’t you and I, once the boys go to bed, why don’t we play a game of Risk,’” recounted Armstrong. “I said I’d enjoy that. We started playing Risk and then he slipped me a piece of paper and said 'read that’. I did.”

“On that piece of paper there was 'That’s one small step for man, one giant leap for mankind’. He says 'what do you think about that?’ I said 'fabulous’. He said 'I thought you might like that, but I wanted you to read it’.”

Dean Armstrong’s testimony nearly seemed to corroborate the long-held opinion of some skeptics that the iconic astronaut had not originally intended to include the article in his line. But Dean Armstrong quickly corrected himself.

“It was 'that is one small step for A man,’” he clarified.

Christopher Riley, a professor of science and media at Lincoln University who directed the documentary, said that Dean Armstrong’s admission reveals that his brother likely gave the line more thought than he ever let on.

“I think the reason he always claimed he’d thought it up after landing was that he was bombarded by suggestions in the run up to the mission, and found them a distraction to the business of landing on the Moon,” said Riley. “It was probably easier to just say that he’d thought it up after landing, thus dodging the issue of where the words came from, and who maybe suggested them, or influenced him.”