In a rare interview, Dean Armstrong recalled that his brother slipped him the words — including the long-disputed reference to “a man” — on a piece of paper as they played a game of Risk, months before the Apollo 11 launch in July 1969.

“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 is quoted as saying in a Telegraph report on the documentary, titled “Neil Armstrong: First Man on the Moon.” The show premiered tonight on BBC Two…

The interview also confirms that Neil Armstrong meant to say “one small step for a man” — even though the “a” wasn’t audible in the transmission from the moon. That’s an important stylistic point, because the “a” draws a contrast between the physical length of a human’s footstep and Apollo 11’s “giant leap” for human exploration.

After the flight, Armstrong insisted that he intended to say “a man.” Some experts say that the “a” was dropped because of a glitch in the radio signal, but most assume that Armstrong just left out the word. As the years went on, Armstrong’s comments on the mystery took on an air of ambiguity. “We’ll never know,” Neil Armstrong told an interviewer in 1971.