Ex-WWE Star Rob Van Dam: Dammmmm His New Girlfriend's Hot!!!

Wrestler Rob Van Dam jumped back on the horse quickly after ending his 17-year marriage, and with good reason.

Rob's dating professional wrestler Katie Forbes ... we're told it's been going on since May ... around the time his wife filed for divorce.

It's not like Swifty and Hiddleston, allegedly -- we're told Rob and his ex, Sonya Szatkowski, had been separated for a while before Rob hooked up.

Rob and Katie met back in April at a wrestling convention -- at adjoining signing booths.

We know her sign ... flames.