"I didn’t meet her until the actual wedding," the photographer told Fox News Digital. "David asked me to do a reading at the wedding. And I was so nervous that I said no. I said, ‘Can’t you get [our friend] Eric [Idle] to do it?’ 

"David said, ‘No, people will assume he’s going to be funny, and he’s already doing a speech at the reception. Come on, Geoff. I want you to do it.’ I came around and said yes. But I have to tell you, it was one of the hardest things I’ve ever done in my life. And I performed at Madison Square Garden.

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"The ceremony took place in Florence," MacCormack added. "We were all in this wonderful hotel by a river. That’s when I met Iman for the first time. We had this funny exchange about bad luck at weddings and whether David should see her the night before. Her sense of humor was so great. I immediately thought to myself, ‘That’s exactly what my pal needs.' Beauty is something, but a sense of humor is everything. That’s when I knew she was ‘the one,’ and David never looked happier."

The songwriter and producer, who shared a friendship with Bowie for over 60 years, is now unveiling over 150 rare and unseen photos of the late star in a "photographic memoir." The book, "David Bowie: Rock ‘n’ Roll with Me," explores how the two became fast friends, their years on the road and what their final goodbye was like. It features an afterword by Bowie himself, who encouraged him to release a book about their adventures together before he died.

"We knew each other from the time we were eight years old until he died," said MacCormack. "I knew him all my life. It’s perfectly ridiculous. He was a wonderful and funny guy. He was my second-oldest friend. The book is a humorous one about how two friends went on this journey together influenced by music."

As children, the boys bonded over having brothers who were in the Royal Air Force. Their siblings had introduced them to artists like Duke Ellington and Ella Fitzgerald, which led to their love for music.

"We fell in love with American music at such a young age," said MacCormack. "We were in England, and here was this great, colorful music from America. You had Little Richard in his regalia and his feet up on the piano, and Elvis Presley singing ‘Hound Dog.’ It was like this wonderful secret that had been kept from us that blew our minds."

As Bowie embarked on a music career, MacCormack was there every step of the way. MacCormack even sang backup on several of Bowie’s albums. And when Bowie was gearing up to hit the road in 1973, he made an offer that MacCormack couldn’t refuse.

"Joining David on tour was magical," MacCormack explained. "He told me I was joining the band. He didn’t ask me. He said, ‘You’re joining my band, and you’re coming to New York, and by the way, I don’t fly, so we’re going by ship. It was just pretty ridiculous really. And I’d always wanted to go to New York. Always wanted to go to America." 

"Hitting New York after five days at sea was mind-blowing really. David had been there before. I remember the car journey to… the Gramercy Park Hotel. And on the way from the docks, David was pointing out this and that. It… was the most exciting thing I’d ever done."

"It wasn’t an overnight success. David tried for years and years with all kinds of art forms," MacCormack reflected. "He was knocking on a lot of doors, which wouldn’t open. But there was a period, about 1971 and onwards, where everything seemed to click into place." 

"His management was great because they said, ‘Look, you’re going to be a star. All [we] want you to do is to create music and do what you’re supposed to do. [We] will take care of the finances.' He was given the freedom not to worry about debts and paying bills. All he had to do was be creative… The ‘70s just flew in."

The London-born entertainer, who had striking androgynous features, quickly made heads turn with a look that was out of this world.

Bowie turned the music scene upside down with the release of the 1972 album, "The Rise and Fall of Ziggy Stardust and the Spiders from Mars," which introduced one of music’s most famous personas. "Ziggy Stardust" was a concept album that imagined a rock star from outer space trying to make his way in the music world. The persona — the red-headed, eyeliner-wearing Stardust — would become an enduring part of Bowie’s legacy and a touchstone for the way entertainers packaged themselves for years to come.

While on tour, MacCormack picked up his camera and began to photograph their travels. He chronicled behind-the-scenes moments during the filming of 1976’s "The Man Who Fell to Earth" and the album "Station to Station," which was released that same year.

MacCormack insisted Bowie wasn’t a typical rock star.

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"We were pretty good," he chuckled. "We weren’t kind of thuggish. David and I were polite, English boys brought up nicely. We got up to stuff, believe me. But that kind of male bravado wasn’t really us. We left that to the roadies… His humor was quite silly. It was a very British thing… He was funnier than most people realized. He had a serious side because he had such an inquisitive mind. He was always inquiring, always reading… Although he was serious about many things, he was also quite funny."

Many of MacCormack’s favorite memories of Bowie take place in New York City, where the singer happily lived with Iman and their daughter Alexandria. He kept a low profile over the years and relished being another face in the crowd.

"He was quite private, and his life was quiet," MacCormack explained. "He didn’t have that star thing to him… He was the kind of guy you would bump into on the street. New York was good to him, and it didn’t give him too much trouble. He was able to have his privacy and move around. That’s what he loved about New York more than most places in the world."

MacCormack last spoke to Bowie a month before he died. At the time, the star was privately battling cancer.

"He was sending me a few pictures of the people we knew," he recalled. "Some of them were no longer alive. I think he was possibly looking back at his life and reminiscing. He was looking back fondly."

Today, MacCormack chooses to remember the happier moments of their time together. It’s what Bowie would have wanted, he said.

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"We had a relationship that was of fun, of closeness," he said. "It was one of humor. I'm just thankful he shared some of his journey with me."

The Associated Press contributed to this report.