EXCLUSIVE

Laremy Tunsil's stepfather tells TMZ Sports ... he is NOT the person who hacked the football star's Twitter account and published a video of Laremy hitting a bong.

FYI -- the video, showing Laremy hitting a gas mask bong, was released on Laremy's own page just as the NFL Draft started. Laremy was expected to be a top 10 pick. Tunsil's agent has said he was hacked.

Since Laremy is currently locked in a nasty legal war with his stepfather Lindsey Miller -- with the two sides filing domestic violence charges against each other last year -- most people began pointing the finger at him.

But Miller tells us he absolutely denies having ANY involvement in the video leak.

"I don't know nothing about no video. I'm not even watching the draft."

Miller says he's upset about being accused -- and adds, "I was a Red Cross volunteer of the year. I would never do anything like this."