Jen's Heartbreak As Justin Theroux & Emma Stone 'Get Serious'

Justin Theroux and Emma Stone's romance is heating up RadarOnline.com has learned exclusively, much to the heartbreak of Jennifer Aniston.

"They're holding back on going totally public just yet, until the terms of Justin's split have been fully worked out. But they're totally dating under the RadarOnline.com, and everyone knows including Jen who's predictably fuming," snitched a source.

Theroux, 46, and Stone, 29, were recently spotted together in France, where they attended Louis Vuitton's fashion show. Though they sat apart on the A-lister filled front row, they were soon caught canoodling at the ritzy after party.

A source told RadarOnline.com exclusively that while the pair did their best to look friendly at the Hotel in Cap-d'antibes bash in Antibes, France, they couldn't keep their hands off each other.

"Aniston considered Emma as a good friend before all this, so it's totally sideswiped her; even though Justin's shameless networking deep inside her social circle has been going on a while.

Theroux was first caught with Stone when he posted a photo of himself hanging out with her in April, just weeks after his split from Aniston!