The romance between Melissa Rivers and porn king Steve Hirsch has officially come to an end.

Sources close to the former couple tell us the two recently called things off ... because they each had too much stuff going on in their personal lives to focus on a relationship.

We're told the split was mutual ... very amicable ... and the two are still friends.

TMZ broke the story ... Hirsch -- president of Vivid Entertainment -- began dating Rivers back in December after meeting through mutual friends.

Now that Melissa has dabbled in porn, the possibilities are now end-less.

Melissa Rivers is used to the awards show circuit, but now that dates porn king Steven Hirsch ... those awards show have a more XXX feel to them.

Rivers and Hirsch hit up the AVN Awards (pretty much the Oscars of porn) in Las Vegas last night. The couple happened to run into Joe Francis in the lobby of the Hard Rock Hotel, where the show was being held.

Just imagine the questions she and mom Joan could have asked last night ...

Joan Rivers couldn't be happier her daughter is dating the god of sex tapes Steve Hirsch -- telling TMZ Live, Melissa Rivers and her new XXX man are a perfect fit ... in more ways than one.

Joan tells us, not only is Steve crazy about Melissa -- "He makes a great living ... and he's Jewish."

But Melissa -- who hooked up with Steve through a friend -- isn't the only one reaping the benefits of her new relationship ... Joan adds, "I'm 78 years old and now I get a discount on lubricant."

TMZ broke the story -- Melissa and the Vivid honcho have been dating for a couple weeks now -- and sources tell us ... "The relationship is going great."

Joan Rivers' only daughter Melissa has been meeting with the king of celebrity sex tapes Steven Hirsch ... but it ain't to star in a XXX flick, TMZ has learned the two are actually dating.

Sources close to the couple tell us Melissa -- who runs "Fashion Police" on E! -- has been dating the Vivid Entertainment honcho for a couple of weeks ... after meeting through mutual friends. 

One person with direct knowledge of the situation tells us, "The relationship is going great."

Hirsch has brokered nearly every major celebrity sex tape on the market ... including Kim Kardashian, Shauna Sand and Chyna ... but he's never starred in one ... so don't get your hopes up.