Forstmann was the head of sports and modeling talent agency IMG among other business endeavors. He bought, sold and turned around dozens of companies including Gulfstream, Aerospace, Dr. Pepper and General Instrument.
The billionaire, who recently ranked No. 242 among America's 400 Richest, grew up in a wealthy family in Greenwich, Conn., the grandson of a German-born wool magnate.
He founded Forstmann Little in 1978 with his brother Nicholas C. Forstmann and, as of 2011, his net worth was estimated at $1.8 billion.
Forstmann never married, though he's been seen with Lakshmi on several occasions over the last several years.
Their relationship blew up in 2010 when Lakshmi, 41, gave birth to her now one-year-old daughter Krishna, leading to speculation over who fathered the child. Later, it was revealed that the father was venture capitalist Adam Dell, brother of Dell computer firm founder Michael Dell.
Lakshmi's relationship with Dell ended in 2009 after he claimed the former model and Bravo host launched a cruel attack on him during a phone call, calling him an unambitious man with an uninteresting career and unmemorable friends.
According to court papers, she also told Dell that she wished her child was from her other lover, Forstmann. Dell claimed this was why she refused to put his name on the birth certificate.
Though a Forstmann spokesperson declined to comment at the time, a source close to him said, He has been carrying out the role of father since the moment Krishna was delivered into his arms.
Lakshmi, India's first wildly successful international supermodel, is known for having a propensity for dating powerful men. For three years, she was married to prize-winning author Salman Rushdie. More recently, she's been linked to New York City nightlife impresario Nur Khan and actor David Spade.
Forstmann himself was no stranger to the tabloid press. He was often photographed arm-in-arm with models and actresses like Elizabeth Hurley, and even dated Princess Diana for a time. Their relationship ended soon after it began, but the two remained good friends until her death. According to The Diana Chronicles by Newsweek and The Daily Beast editor Tina Brown, the two were plotting to wed in the last weeks of her life.
Forstmann was diagnosed with brain cancer and received treatment at the Mayo Clinic in May. He vowed to fight the disease, telling The New York Times soon after his diagnosis This is not how I want to end. It's a bend in the road for me.
It seems the end came far too quickly.
He is survived by his two sons, Siya and Everest, brothers Anthony and John, and sisters Marina Forstmann Day and Elissa Forstmann Moran.