Crystal Hefner joined us Tuesday on "TMZ Live" and we asked her about her wanting to drop Hef's famous last name and get back to her roots ... even though she's become famous as a Hefner.

Hugh's third and final wife says the name change is all about getting back to who she really is ... telling us she became a totally different person when she was with Hef ... basically molding herself into the image he wanted.

Crystal, who was married to Hugh when he died in 2017, says it took her years to realize her life at the Playboy Mansion wasn't all it was cracked up to be ... she says she started seeing things differently only a couple of years ago when she started writing a new memoir.

In her new book, "Only Say Good Things: Surviving Playboy and Finding Myself," Crystal kinda trashes her husband and life inside the Playboy Mansion. From her view, of course, she's just speaking her truth.

Looking back now, Crystal insists she was hypnotized by Hef's Playboy image and lifestyle ... telling us she didn't expect him to be a misogynist the way she claims he was.

Crystal says she went in thinking Playboy was all about freedom, but ultimately felt like she was trapped at the Mansion. Now that she's out and Hef's been dead for over 6 years, Crystal wants to get back to her roots as Crystal Harris.

As we first told you ... Crystal says Hef's secretary changed her name to Hefner shortly after their 2012 marriage at Hugh's behest ... and now she feels like the famous last name isn't helping her much these days, and she wants a fresh start.

It's an interesting look at a different side of Hef and the Playboy Mansion ... Crystal says she wasn't physically attracted to Hugh and tells us all about the moment she realized he wasn't deeply in love with her.