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. Gallery Launch Gallery

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. Getty

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