Credit: Chris Jackson/Getty Images Photo: Russell Brand and Katy Perry Attend the European Premiere of Arthur on April 19, 2011 in London, England

The relationship rumor mill has been churning ever since Hollywood power couple Katy Perry and Russell Brand were photographed separately on Christmas day … sans wedding rings. And now, a source close to Katy and Russell is revealing details about the alleged fight that drove a wedge in their yuletide bliss.

According to Us Weekly, Katy was supposed to fly her entire family to Russell's London home, but instead headed to Hawaii with friends.

"They had a massive fight," the insider dished. "She was like, 'F--k you. I'm going to do my own thing.' Russell replied, 'Fine, f--k you too.'"

According to a second insider, it was more than just a petty argument. "Katy doesn't think Russell respects her parents' Christian beliefs or her friends," they said.

Kate, who grew up in a devout Evangelical household, began singing in church and even recorded a gospel album back in 2001 under the name Katy Hudson.

While the 27-year-old Grammy-nominee spent the Christmas holiday splashing about in an itsy-bitsy bikini just off the coast of Kauai, her British hubby, 36, chatted with mates at a local pub in Coverack, Cornwall.

"They haven't split up just yet, but things are not good," the first source added. "The fighting is getting worse."

Source: Us Weekly