"Guess who I had lunch with today.I KNOW!" the 55-year-old actress captioned the shot.
Cox often posts photos with Friends castmates Lisa Kudrow and Jennifer Aniston, but it's not often the show's men make an appearance.
"Could I BE any happier?" Aniston, who was seen as Rachel Green in the show, joked.
While Jennifer also penned, "I LOVE YOU, GUYS", in the comments, she addressed her absence as she spoke with Entertainment Tonight at the SAG-AFTRA Foundation's Patron of the Artists Awards in Beverly Hills later that evening. "Lucky lucky. #beautifulpeople", wrote Lisa.
The actors took on the roles of Joey Tribbiani, Ross Geller and Chandler Bing in the now iconic TV show.
In the picture Jennifer, Courteney and Lisa were joined by their former cast-mates Matt LeBlanc, 52, David Schwimmer, 53, and Matthew Perry, 50. She had said, "We would love for there to be something, but we don't know what that something is".
Aniston had recently hinted that the cast might reunite, even if it's as part of a different project.
Aniston, who now has 18.7 million followers on Instagram, told Los Angeles Times that she keeps different mobile phones for office and work to avoid getting hooked on the internet."I won't let it be addictive". "Oh god, there's a lot of different ideas", Aniston told ET, "but who knows?" I made a decision to get two different phones.
Just yesterday, Courtney, shared a picture of her own Instagram account, in view of her 5.8 million followers, which showed her with Matthew, who played her on-screen husband Chandler. She has received over a million likes each on her two posts.