The reality TV star shared some steamy details about her bedroom antics with the content creator -- a member of the popular Montana Boyz group -- during a recent episode of KC's "Let's Be Honest" podcast.

As Kristin put it ... Mark is the "best sex" she's ever had -- though, she's not giving Mark all the credit.

According to Kristin, a lot of women find sex gets better with age ... noting insecurity in youth plays a factor in underwhelming activities in bed.

She continued ... "I’ve let all of that go and I think I am more present physically during sex than I’ve ever been. And, I’m so wildly attracted to you. And, I just think we have really hot sex."

Listen to the clip ... Mark expressed a similar sentiment about their sex life ... noting Kristin was also his best bedroom partner to date.

This certainly left KC feeling good about herself ... as she confesses this is the first time Mark ever shared this with her.

Kristin was previously married to NFL star Jay Cutler, with whom she shares sons Camden and Jaxon, and daughter Saylor. Prior to dating Mark, the "Laguna Beach" alum was also linked to comedian Jeff Dye and country singer Chase Rice.