The Gunners are preparing to face London rivals Chelsea in the Europa League final later this month.
This London derby has seen some incredible moments throughout the years.
One of them was a clash between Gunners hero Diaby and Chelsea captain Terry.
Playing in the 2007 League Cup final, the Englishman was knocked out when the midfielder tried to clear a corner kick.
The Arsenal man's boot connected with Terry's chin at the Millennium Stadium.
But footage has emerged of the former Gunners star making a huge revelation about the incident.
Speaking on the club's official YouTube channel, Diaby said: “I was really scared.
“I thought I'd killed him. I was on my knees. You can see pictures of me praying.
“He was laying down, unconscious. But someone came over and said he was ok.
“I had to go out after because his chin is very strong.”
The former midfielder went on to reveal a frightening prediction he made before the final.
“It's strange,” Diaby added. “A week before the final, I was watching a game with my brother.
“I think Chelsea were playing Newcastle. I could see [Terry] was putting his head in at the free kicks.
“The defender was kicking the ball and I said to my brother 'this guy is crazy'.
“'One day, someone will kick his face'. And the week after, it was me.”