PORTIA DE ROSSI may have been laughing in the now-famous photo of wife Ellen DeGeneres gawking at Katy Perry’s boobs at the Grammys but sources say it was all an act – and that she’s fed up with Ellen’s flirting!

In fact, The ENQUIRER has learned that the “Arrested Develop­ment” star “threw a jealous hissy fit” backstage after the ogling incident, and she warned the Emmy-winning talk-show host to knock it off – or else!

ELLEN HAS HAD A CRUSH ON KATY ever since (her debut song) ‘I Kissed a Girl’ hit the radio,” said an insider. “Portia used to think it was cute, but it’s starting to get old, and she thinks Ellen took it way too far at the Grammys.

“She’s worried that Ellen may want to kiss Katy for real!”

The 28-year-old “Firework” sing­er flaunted her trademark curves in a low-cut, figure-hugging mint-green Gucci gown at the Feb. 10 awards show where a photographer snapped a picture of Ellen staring at Katy’s ample cleavage. Ellen got such a kick out of the photograph that she posted it on Twitter.

Portia played it cool publicly, but she pulled Ellen aside a few minutes later and “gave her an earful about what’s funny and what isn’t,” said the source.

Ellen, 55, and Portia, 40, wed in 2008 but, as The ENQUIRER previously reported, sources say they’ve hit a few rough patches as Ellen devotes more and more time to her soaring career.

Meanwhile, Katy, who di­vorced British comedian Rus­sell Brand in 2012, is cur­rently dating notorious la­dies’ man John Mayer. But that apparently means little to Portia right now.

“Portia feels threatened by Katy – she’s hotter, younger and has huge boobs,” said the source. “So she’s setting ground rules for Ellen and Katy’s friendship – no hanging out one on one, and no more ogling!”