Gianni Versace's Partner Opens Up About Life 21 Years After Finding His Body in Shocking Murder

The depression Antonio D’Amico endured after the shocking July 1997 murder of his longtime partner Gianni Versace lasted eight years.

D’Amico, a model and designer, found the fashion icon’s body in a pool of blood outside the couple’s Miami Beach, Florida, villa after hearing gunshots. He subsequently fell into a “black pit,” he tells PEOPLE in an exclusive interview.

“When Gianni died, I was cut in two,” says D’Amico, now 59, about the slaying that’s the subject of Monday’s episode of People Magazine Investigates: Crimes of Fashion, airing at 9 p.m. ET on Investigation Discovery.

Versace was not just D’Amico’s partner, he was also his professional mentor. D’Amico worked at Versace’s offices and “spent 24 hours a day with him” as the couple divided their time among the designer’s opulent homes in Milan and Lake Como, in Italy, and in New York and Miami Beach.

“For me it was like going to school and learning from the best teacher you can have,” D’Amico says.

• Watch People Magazine Investigates: Crimes of Fashion — The Murder of Gianni Versace, airing Monday at 9 p.m. ET on Investigation Discovery.

D’Amico says that behind the fanciful grandeur of Versace’s designs was a tireless, practical work ethic.

He also tenderly remembers Versace’s quirks, such as his messiness around the house, which contrasted with D’Amico’s tidiness, and the way he would often “have his head in the clouds” and become forgetful. He was a homebody despite his superstardom, D’Amico says, and he was a terrible cook — despite coming from the south of Italy, a region famous for its cuisine.

The couple met in 1982, but their life together ended when 27-year-old Andrew Cunanan killed Versace as part of a four-month spree, during which he murdered at least four others.

After years of grieving, D’Amico ultimately realized he needed to move on and find happiness without Versace.

“Of course I never forgot. But I took my life in my hands and I started over again,” he tells PEOPLE.

• For more on the shocking murder of Gianni Versace and the devastation of partner Antonio D’Amico, subscribe now to PEOPLE or pick up this week’s issue, on newsstands Friday.

D’Amico began another relationship and currently lives quietly in Milan with his partner of 13 years, Alberto Santinelli. He has no contact with the Versace family, with whom he settled a dispute over Gianni’s will in 1998.

He also threw himself into his work, and his new Antonio D’Amico Golf line of men’s and women’s sportswear launched this year.

“My work was instrumental, fundamental for this,” he says. “It helped me put aside all the pain, the grief and forget for a moment in a bid to have a new objective.”

He adds, “This collection is my new beginning.”

People Magazine Investigates: Crimes of Fashion — The Murder of Gianni Versace airs Monday (9 p.m. ET) on Investigation Discovery.