NOT only was the brutal knockout which floored actor Michael B. Jordan during filming for the latest Rocky movie real — he agreed to it.

Sylvester Stallone has revealed the brutal punch was part of an initiation all actors in the long-running film series take part in.

“When you do a Rocky film for some reason we’ve decided to have this kind of initiation that you have to get clobbered,” said Stallone, during an appearance on The Tonight Show starring Jimmy Fallon.

“So Michael B. Jordan says ‘I’m part of the Rocky family’ and I said ‘no, you’re kind of like Dead Man Walking because unless you take the shot, you really can’t be part of the family’. He says ‘well bring it on’.

“So I go to the other fella (British boxer Tony Bellew, who plays “Pretty” Ricky Conlan), who is a world champion, and I said ‘just give a little hip to it’.

“Now when a real pro hits you, it isn’t like you see in these bar-room brawls or these Westerns with a big punch. It’s ‘boom,’ and next thing you know you are talking to angels.”

If you’re yet to see the footage, this is the moment Jordan saw stars.

Michael B Jordon, "young creed and "getting KO'd for real! But he got up and did it again! That's called guts!! pic.twitter.com/yFo3PVmvhA — Sylvester Stallone (@TheSlyStallone) December 9, 2015

Jordan spoke about the blow during an appearance on Bill Simmons’ podcast. “All of a sudden, you just hear this snickering from the corner, and everybody’s like, ‘What?’ Sly goes, ‘Man you’ve got to take it.’ I said, ‘What do you mean?’ He said, ‘No, you’ve got to take a real punch,” Jordan said.

“I had to really get hit. And legally, Ryan (Coogler) — he’ll definitely tell you this — as a director, he can’t legally say, ‘Take the punch.’ So I had to willingly step up and say, ‘Alright, I’ll take the hit.’ But I definitely got peer pressured. The hit is pretty epic. I was smelling canvas.”

But it’s not like Stallone was asking Jordan to do something he’d never done before. The now 69-year-old took an heavier shot from actor Dolph Lundgren during filming for Rocky IV.

“Dolph Lundgren put me in the hospital for four and a half days,” Stallone told Fallon. “It was unbelievable. He hit me so hard in the chest that the next thing I knew I was on a low-altitude flight to intensive care at St. John’s Hospital surrounded by four nuns!”

You can watch the interview in the video below.