A kitchen porter at Fishmongers' Hall single-handedly fought off the terrorist who launched an attack at the historic building near the north end of London Bridge on Friday, the CEO has told ITV News.
Kitchen porter Lukasz ran towards "trouble" after hearing a "spine chilling" scream while he was washing up, Toby Williamson said.
Lukasz sustained several stab wounds in a "brutal" fight with terrorist Usman Khan, after arming himself with a long stick he had ripped from the wall, Mr Williamson explained.
Despite having a badly injured left arm, Lukasz continued to fight until the terrorist was brought down on London Bridge, following Khan out of the building and yelling at passers-by to get out of his path.
Mr Williamson said Lukasz's bravery and quick thinking helped give others time to escape as he took on the terrorist solo.
Commodore Williamson had stepped out of the building just half an hour before the attack began, but he spoke to staff over the weekend to get a clearer picture of how events unfolded.
"The story really begins with a guy called Lukasz who is doing the washing up downstairs. He hears this spine chilling shout. As he's a first aid trained person, he makes a choice, he goes upstairs towards trouble.
"It's pretty clear what's happening. There's a bad guy with knives doing stuff and people fighting for their lives. Lukasz rips off the wall this long stick and charges in towards the terrorist.
"He gets him, right in the chest, but it bounces off - he's clearly got some sort of protective vest, which we now know was some sort of suicide vest underneath."
"But he's (Lukasz) buying time. He's allowing others to crawl out the way and find a bit of space.
"And he's got a minute, a long, long minute - one-on-one knife fight. It's pretty brutal. The terrorist comes up, he's armed, and eventually he (Lukasz) gets five different slashes and stab wounds up here (points at upper arm)."
Commodore Williamson says contrary to media reports at the time, Lukasz was not armed with a Narwhal tusk, but confirmed the ornament was used to fight the terrorist by another individual who took it from the walls of Fishmongers' Hall and, along with another man with a fire extinguisher, joined Lukasz in tackling the terrorist.
Outnumbered, Khan ran down the stairs of the building, but was unable to get out the front door. He then headed to the reception in a bid to flee.
"Gareth, our doorman is just trying to hold him off, whilst, Dawn, the receptionist is getting on with the emergency calls, setting off the alarms, doing everything's she's trained to do. What a brave person she is," Commodore Williamson says.
There was then "a showdown in the entrance hall" where Andy, a maintenance engineer, tried to stop Khan before being stabbed in the chest and forced to open the door at pain of death.
"(Andy) is a very cool customer," Commodore Williamson said. "He thinks for a moment 'shall I spill it out onto the pavement or am I going to keep this all nicely contained'.
"He does the right thing, he opens the door."
Khan then headed out onto the street with "good old Lukasz" at his heels.
"And he's shouting and screaming and he's getting everyone else out of the way.
"But Londoners don't do that. They know when to join in and help someone. Lukasz is losing strength in his left arm at this point and can't take the fight to the end himself."
Lukasz was joined by several others, including a plain clothes British Transport Police officer, on London Bridge as they scrambled to disarm the terrorist.
The fight was caught on camera by members of the public and show armed police arriving at the scene, pulling the men off Khan and pointing their guns at him as he lies on the floor.
He was shot dead at the scene.
Lukasz, originally from Poland, has worked at Fishmongers' Hall for 10 years, Commodore Williamson said, describing him as a "humble" man.
Former University of Cambridge students Saskia Jones, 23, and Jack Merritt, 25, were fatally stabbed by 28-year-old convicted terrorist Khan in the attack.
Khan was out on licence and wearing an electronic monitoring tag when he launched the violent attack, which injured three others, after he was invited to the prisoner rehabilitation conference on Friday afternoon.