11:03 AM PT -- We've learned Jackson -- who goes by J.T. -- was an actor and close friend of Kevin's for more than 15 years. Jackson was in "S.W.A.T.," "Naked" and even in Kevin's movie "Think Like a Man Too." The two have posted several photos together through the years and J.T. even attended Kevin's bachelor party.
Kevin tweeted, "Mind blown ... Hurt ... at a loss for words and simply in complete disbelief at the moment. WOW."
The man who allegedly tried to coerce Kevin Hart into paying him for a sex video has been charged with extortion.
Jonathan Todd Jackson faces 2 felony counts -- attempted extortion and extortion by threatening letter.
Jackson is accused of trying to extort an undisclosed amount of money from Hart, in return for keeping the video secret ... a video showing Hart with a woman in his hotel room in Vegas apparently having sex.
The liaison went down last summer. The video is 4 minutes and 47 seconds long and highly produced. As we reported, both Kevin and the woman claim they had no idea they were being filmed.
Kevin's wife was pregnant at the time and he apologized to her and his family on social media.