Madonna and John F. Kennedy Jr. "had a flirty and friendly banter," a friend of the president's son tells PEOPLE
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Fans know her today as “Madge” or the “Queen of Pop,” but there was a time when Madonna was referred to simply as “M” – a nickname that, as it turns out, her one-time love interest John F. Kennedy Jr. claimed as his own.

A friend of the late John F. Kennedy Jr.’s tells PEOPLE of the connection between the pop star and former President John F. Kennedy’s son, “It was a flirtation, and when other people referred to her as M around that time, just by her first initial, he would say, ‘I started that.’ He called her M when he wrote or faxed her. There were no cell phones then and he was always very territorial that he started that moniker for her.”

Previously untold details about JFK Jr.’s private life are the subject of an intimate new documentary, I AM JFK Jr., airing Aug. 1 on Spike TV. The film features interviews and stories from those who knew the president’s son best, including famous friends like Robert De Niro, Cindy Crawford and Mike Tyson.

The documentary paints a portrait of a man who, as De Niro puts it, “lived his life the way he wanted to” and forged his own legacy, apart from his father’s.

It’s no wonder, then, that JFK Jr. was drawn to Madonna. “I think she gave it right back to him and she teased him and she was irreverent and he liked it,” the friend tells PEOPLE.

The spark between Madonna and JFK Jr. never amounted to much, however, eventually fizzling out due to their busy schedules.

“The flirtation kind of continued and they would try to get together but it was hard because she was on tour and he was working,” JFK’s friend explains. “They saw each other a few times and they had a flirty and friendly banter but it wasn’t a ‘relationship.’ ”

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“They would fax notes back and forth – they might have gone out twice but from what he said, it was, ‘We could never get together’ and then it kind of faded but they stayed friendly.”

I AM JFK Jr. premieres on Monday, Aug. 1 at 9:00 p.m. ET/PT on SPIKE TV. It will also be released in select movie theaters beginning July 20.