Although the pair were said to be having "normal couple problems" before the actor-and-comedian filed for divorce on December 30 - just over a year after they first tied the knot - Katy reportedly had no idea Russell was considering ending their marriage for good.
A source told HollywoodLife.com: "Katy and Russell were having normal couple problems. There was no talk of divorce around Thanksgiving. It all happened right before Christmas but no one, not even Katy saw the divorce coming."
While the singer is said to be "devastated" at the marital split, the insider added that there is "zero chance" of the couple rekindling their romance.
Russell recently admitted he found it hard not to "cherish and crave" his wilder days before he met Katy.
In an interview recorded shortly before the couple's split, he said: "I'd do a gig and four or five women would come back.
"There were times when it wasn't all desperate and ugly. There were times when I was this representation of pure libertarianism and sexuality. It's so hard not to cherish them and crave them.
"I know where they ended up. I know where they went, but I became this thing. Women meeting across me. One would leave, another would come. There'd be crossovers. And they had no problem with each other. And it was blissful."