On Thursday, Moore, 56, shared a photo of the ladies posing for the cameras and people couldn't help but notice the friends' similarities with their striking dark hair and black-rimmed glasses.
"Are you relatives," one commenter asked.
"Wow y'all look like twins," echoed another person.
"Sisters," one fan wrote. "Twinning," one person added.
"Demi and Courteney!! You both look like twins," another person wrote.
"Twinsies and gorgeous," one commented.
For the picture, Moore opted for a black turtleneck tank paired with denim overalls, while Cox, 55, rocked a black button-down with black pants.
Moore has been gearing up to release her new memoir titled "Inside Out" -- out next Tuesday -- which her publisher has called "deeply candid and insightful."
According to HarperCollins, the actress wrote openly about everything from her "tumultuous relationship" with her mother, from whom she was long-estranged, to her three marriages, among them to Bruce Willis and Ashton Kutcher.
Fox News' Sasha Savitsky contributed to this report.