Flavor Flav Says Miley Cyrus Jokingly Slapped Him For Calling Her Gwen Stefani

Gwen Stefani ... getting a swift slap to the face -- but one all in good fun he says.

The Public Enemy rapper talked about the incident on a recent episode of "Just B with Bethenny Frankel" ... where he revealed he ran into her several years ago when she and Gwen apparently had similar haircuts.

Flav said he got super excited to meet Gwen and ran up to her ... only to find himself accidentally speaking to Miley instead.

He says MC played it super cool, just going along with it during the convo as he lauded her for all of GS' work ... an embarrassing moment for FF when his friend later told her it was actually Miley.

Flavor Flav says he went right up to Miley to apologize, adding of course he knew her and her dad Billy Ray ... which is when he got the smack right across his face.

He says the moment didn't create any animosity ... instead, he and Miley laughed off the moment, and the two even met up backstage of the Grammy Awards this year.

But, Miley couldn't resist giving Flav a little bit of guff over the past mistaken identity.

A video went viral from their meetup which showed the two hugging it out while Miley joked he always used to call him Gwen ... so, clearly this is still stuck in her mind.