Bowie died on January 10 last year in New York City due to liver cancer, shortly after the release of his 25th studio album, Blackstar.
Iman's heartfelt tribute comes after a new BBC documentary has revealed Bowie only discovered his cancer was terminal three months before he died, as he was starring in death-shrouded music video Lazarus.
Speaking on David Bowie: The Last Five Years, director of the music video Johan Renck, said: "I found out later that the week we were shooting is when he found out that it is over.
"We'll end treatment or whatever capacity that means, that his illness has won."
Renck added that the video, which features Bowie lying in a bed with his eyes covered by bandages and replaced with buttons, was not about the singer's illness.
"To me it had to do with the biblical aspect of it, you know the man who would rise again, and it had nothing to do with him being ill.
"That was only because I liked the imagery of it."
The Last Five Years looks at Bowie's acclaimed A Reality Tour in 2003 as well as the last four years of his life in which he returned with two albums after a 10-year absence and helped produce hit musical Lazarus.
It includes rare and never-before-seen footage of Bowie and interviews during his Ziggy Stardust characterisation and is a follow-up to the acclaimed David Bowie: Five Years, which was broadcast in 2013.
In one early interview, Bowie is asked if he always wanted to be famous, to which he replies: "Yeah. It's more than being a star.
"What it is really is that I want to be productive. I'm not content to just be a rock 'n' roll star all my life. I am trying to be one at the moment because I need it at the moment for a particular reason so I can get off and do other things."
There are also interviews with his long-time producer Tony Visconti who said Bowie was "at the top of his game" when recording Blackstar. Visconti, the man behind more than half of Bowie's studio albums including The Man Who Sold The World and Heroes, added: "David had great, grand ideas. "To become well known, famous, for him was initially to have the resources to realise what his ideas were. He really does come from that spirit, he just didn't want to be famous per se."
