Christopher Steele said an obscene video, described in a dossier he compiled, 'probably exists.'
He speculated that it remains unseen, despite intense interest, because Russia had no need to show it.
Steele said that Russia got "pretty good value" from the Trump presidency without blackmailing him.
Christopher Steele, the former British spy behind a heavily disputed dossier on Donald Trump, said he believed an infamous "pee tape" of Trump does indeed exist.
In an interview with ABC News, he speculated that Russia may have kept the tape hidden because Trump offered them "pretty good value" during his time in office.
Steele made an unsubstantiated allegation in the 35-page dossier, which was compiled during the 2016 presidential election that Russian authorities had covertly filmed Trump being urinated on by prostitutes at a Moscow hotel room in 2013.
"I think it probably does [exist]," Steele told host George Stephanopoulos in an excerpt of the upcoming documentary "Out of the Shadows: The Man Behind the Steele Dossier."
Pressed on why Russia wouldn't have used such leverage, Steele replied: "Because I think it hasn't needed to be released because I think the Russians felt they'd got pretty good value out of Donald Trump when he was president of the US."
While Trump was often criticized for a perceived closeness to Russian President Vladimir Putin, there is no evidence to support the existence of the tape.
Trump, who called the dossier a "pile of garbage" - reportedly most recently denied that specific allegation to a group of Republicans last week in unprompted remarks.
"I'm not into golden showers," Trump told a group of Republicans in Palm Beach, Florida, The Washington Post reported.
"You know the great thing, our great first lady - 'That one,' she said, 'I don't believe that one.'"
The line appeared to be a joking reference to claims that Melania Trump does not always believe her husband's denials of wrongdoing.
Steele's dossier claimed that Trump had in 2013 rented a room at the Ritz-Carlton in Moscow during a business trip to Russia. It said that he then hired prostitutes who performed sexual acts in the room which involved urination, Insider's Sonam Sheth previously reported.
Some of the allegations in Steele's dossier have been partly substantiated over time, but many of the other allegations in Steele's dossier remain unsubstantiated.
Steele admitted to ABC News that he was "prepared to accept" that not all of what he passed on was true, HuffPost reported.
He said: "I stand by the work we did, the sources that we had, and the professionalism which we applied to it."