Miley Cyrus heating things up –and not with Minnie!

The 15 year-old was at LA Fashion Week giving BF Justin Gaston, 20, the tongue as he strutted the man-cat walk.

Miley and Justin "were all over each other backstage," a source told the NY Daily News.  The source also told the NY tab that Miley "was probably staying at Justin’s tonight and that they were going to skip the after-party and have a party of their own."

Miley’s rep denied the report saying the nymphet went home with her mom Leticia and manager.

Celebs like Heidi Klum went virtually unnoticed as Miley entered the event surrounded by a phalanx of bodyguards, according to the NY tab.

"Everyone in LA knows that if you want Miley to show up at your event, all you have to do is hire her boyfriend as a model."

FYI: Although Miley celebrated her Sweet 16 party at Maus Land, she’s still 15 and "dating" a 20 year old.  Purity ring allegedly, still firmly in place.