Ben Affleck, Jennifer Garner's flirtatious hug explained

Ben Affleck and Jennifer Garner are reportedly much more than friendly exes.

Ben and Jen were recently spotted together in a flirty embrace while celebrating their son Samuel's 13th birthday at a paintball park. The Triple Frontier star held his ex-wife while she held a paintball gun.

According to an expert, the embrace should be cause for concern for Garner’s longtime beau John Miller.

Body language expert Patti Wood told Radar Online that the hug "communicates his desire to be sexually intimate or familiarity with her based on their old relationship.”

"His hug is not something you do with an ex," remarked Wood.

"He's wrapping his arm all the way around the front of her body, with the position of his pelvis and ventral (abdomen) front and heart window in contact with her body. It all implies a familiarity and desire for sexual ownership," she added.

According to an onlooker, Affleck held Garner while whispering in her ear.

"Ben and Jen looked like they were having a ball," an insider told the publication. "They were giggling and joking and having a great time. Sparks definitely flew."

"The question is what this means for Jen's relationship with John. He can't be happy to see Ben hugging his girlfriend," remarked another source.

Ben Affleck and Jennifer Garner were married for a decade and share kids, Violet, 19, Seraphina, 16, and Samuel.