As recently as May, Zooey tweeted a picture of her and Kaley, calling them "New best friends".
But it seems things have taken a turn...
The latest issue of Star magazine says the relationship between Kaley and Ryan has deteriorated to the point that the couple have taken to fighting in public. At an engagement party for a friend of Ryan's last week, tensions between Cuoco and Sweeting bubbled over, resulting in an all-out screaming match in plain view of the other guests.
"Kaley looked like she didn't want to be there," said one on-looker. "Ryan told her to relax, and that's when all hell broke loose."
"She snapped back and told him where to go. She didn't know many people at the party and felt like he was being irresponsible not looking after her. It wasn't pretty."
Sources tell the tabloid that the blow-out was just a small taste of what goes on behind closed doors in the Cuoco-Sweeting household.
One insider says that Kaley is insanely jealous of the relationship between Ryan and New Girl star Zooey Deschanel, though Ryan insists they're just friends.
"Ryan doesn't have many friends in LA, so he's reached out to Zooey a few times to get together," says the source, adding that Kaley has now forbidden Ryan to spend time with Zooey.
To think that just last week, Kaley was talking about becoming a mom. Quite an abrupt end to the honeymoon phase.