New details emerged Friday in the shocking suicide of billionaire financier Thomas H. Lee — including how he was found in his office bathroom with a single gunshot wound to his head and his Smith & Wesson revolver next to him, police sources told The Post.

Lee, 78, was discovered by a female assistant on the floor of the bathroom in his office at the Fifth Avenue headquarters of his eponymous financial firm shortly after 11 a.m. Thursday, sources said.

First responders found him lying on his side, fully clothed, with a self-inflicted gunshot wound to the head, they said.

CPR and defibrillation on the scene were unsuccessful, and Lee was pronounced dead at 11:26 a.m., sources said.

The revolver found at his side was registered and licensed to him, sources said. The pistol’s license was in the office at the time, they said.

According to Forbes, Lee was worth an estimated $2 billion when he died.

Lee was so renowned for his backroom savvy that he “was the inspiration for Oliver Stone’s ‘Blue Horseshoe Loves Anacott Steel’ from the hit ‘Wall Street,’ ” said a source who knew the financier to The Post, referring to the code language used in the 1987 flick for character Gordon Gekko and a company he’s eyeing for a buyout.

“But [he] was one of the most generous, and kindest people [I] ever met,” the source said of the tough businessman.

The uber-connected Lee, who was married and had five children, “was regarded as having one of the most admired houses in the Hamptons — Bill and Hillary Clinton were frequent guests, they would regularly stay there,’’ the source said.

“Additionally, although he wasn’t a member, he was a regular at the legendary Maidstone Golf Club.”

In a statement issued Thursday, Lee family friend and spokesman Michael Sitrick said the Wall Street titan’s family was “extremely saddened” by his passing.

“While the world knew him as one of the pioneers in the private equity business and a successful businessman, we knew him as a devoted husband, father, grandfather, sibling, friend and philanthropist who always put others’ needs before his own,” Sitrick said.

A graduate of Harvard University, Lee was perhaps best known for leveraging a massive buyout of Snapple in 1994. He was also an avid art collector with influential pals such as the Clintons, who famously holed up at his Hamptons pad after the 2008 Democratic primary.