Denise Richards & Charlie Sheen Reunite on Red Carpet for Documentary Debut

12:46 PM PT -- Aaron Phypers -- Denise's estranged husband -- is weighing in on Denise and Charlie getting back together for a photo op on the red carpet. Aaron tells TMZ ... "If Charlie knew how many of Denise’s paparazzi tip offs caused him extreme embarrassment and pain, I don’t think he’d fake a smile for a second."

Surprise! Charlie Sheen and Denise Richards just reunited on the red carpet of his new Netflix documentary "aka Charlie Sheen" ... and the pair look like a couple of old pals!

Check out the video from the red carpet Thursday night at the Netflix Tudum Theater in Hollywood -- the exes go in for a friendly hug as soon as they bump into each other. Charlie cracks a joke with photographers, asking if they want them to pose together.

Both stars have smiles on their faces and look totally comfortable with each other ... Charlie even wrapping his arm around Denise's waist.

As you know, the "Two and a Half Men" alum and Denise married in 2002, then went through a nasty divorce in 2006 ... but the pair have totally made up since then.

Charlie even appeared on Denise's Bravo reality show, "Denise Richards & Her Wild Things," back in April for a family dinner with their younger daughter, 20-year-old Lola. They also share Sami, 21.

Their red carpet reunion -- the first they've walked together since 2005 -- comes as TMZ broke the news Charlie donated between $26 million and $30 million to various charities at the height of his career, anonymously.

It also comes as Denise goes through a contentious divorce from Aaron Phypers, who filed for separation back in July and requested spousal report.

The latest update came Thursday when the "The Real Housewives of Beverly Hills" star filed her response to her ex's divorce petition and asked the court to award her spousal support and deny him any from her.

Aaron told TMZ he feels Denise is trying to "humiliate" him with her reponse.