Her triumphant return happened during the season one finale on Wednesday, and fans are losing it over her appearance.
For those who don't remember, Richards played Robin McGill in season two of the original "90210."
She appeared in the episode called "Wedding Bell Blues" where Mel and Jackie get hitched.
Richards' character was Kelly Taylor's cousin. Of course, Kelly was played by Jennie Garth.
Now, let's get back to that steamy makeout session with Ian.
The duo finally see each other after years of separation and their chemistry was magnetic.
Richards and Ian couldn't keep their hands to themselves and who can blame them. It gets messy after they sleep together though.
Ian has been casually dating "BH90210" writer Anna, played by Natalie Sharp, on the show, but couldn't resist a night with Richards.
Once the FOX show gets picked up, everyone celebrates and that's when Ian figures out that Richards is actually Anna's mom and he's dumbfounded.
Yep, that happened.
TV watchers loved seeing Denise Richards back on the show, although some "BH90210" fans had a hard time remembering her character.
"So I googled #deniserichards for confirmation that was her," one fan tweeted. "Cant help but smile from the #90210's nostaglia."
Another person pleaded for the show to come back for a second season, but added, "ease [sic] tell me when Denise Richards was on the original."
Fans are hoping "Beverly Hills, 90210" returns next summer, despite a significant drop in ratings.
It was however the highest-rated new scripted series of the summer, reported The Wrap.