The FBI revealed that viral online footage purported to be of Joaquin “El Chapo” Guzman is indeed the cartel boss — and helps solidify the case against him.

The clip, first uploaded to Liveleak.com in 2015, shows a man sporting a baseball cap tensely pacing back and forth as he questions another man, who appears to be chained to a pole.

“Oh, so that son of a b–ch was the group’s boss? He was the one in charge of all of Mazatlan?” barks the hat-wearing man, identified by FBI agent Stephen Marston as Guzman himself.

The bound man says no, and that the leader of a group identified by Guzman only as “those f–kers” is in Los Mochis, a city in Sinaloa, Mexico.

Marston did not identify the man being interrogated, though he is reputedly a member of the rival Los Zetas cartel. His fate is unknown.

Guzman, on trial in federal court in Manhattan, has pleaded not guilty to various charges, including firearms possession and importation and distribution of cocaine.

In the footage, Guzman appears to be holding something, though it’s not clear what it is.

Amazingly, audio of the interrogation was also caught on an FBI digital wiretap, as someone nearby attempts to place a call. A recording of that call matches the video almost word for word, and places the encounter on April 25, 2011.

Marston said Tuesday he was sure the cap-wearing man was Guzman, given his penchant for the distinctive hat, plus voice recognition.

Jurors were then shown a series of photos of Chapo in his favorite style of cap — and holding semi-automatic weapons.

In one undated snap, Guzman can be seen holding what prosecutors described as a gold-plated AK-47 rifle. In another snap, he is toting yet another semi-automatic rifle.

Marston testified that, as part of the wiretap operation, the FBI managed to record the drug lord between 100 and 200 times.