Hulk Hogan will sue his best friend, Bubba the Love Sponge, for allegedly betraying him by secretly taping Hulk's sexual escapade with Bubba's wife Heather ... TMZ has learned.
We're told ... the lawsuit will be filed in Florida and Hulk will allege invasion of privacy, on grounds Bubba and Heather (also a defendant) conspired to roll tape during her encounter with Hulk.
We broke the story ... in the tape, right after Hulk bangs Heather and leaves the room, Bubba enters and says to Heather, "If we ever did want to retire, all we'd have to do is use this footage."
Hulk said on TMZ Live he was sick to his stomach over the revelation.
Hulk is also filing a federal lawsuit against the website that posted the tape.