For Katy Perry, the late Johnny Lewis was “The One That Got Away.”

A source close to the singer, 27, tells Us Weekly that Perry is “devastated” after learning on Thursday about the death of the Sons of Anarchy actor, whom she dated from 2005-2006.

Even back then, the insider reveals, Perry could tell Lewis was headed down a troubled path.

“She had to separate from him . . . to get ahead and focus on her career,” the source explains. “He was in trouble then and she couldn’t help him. A lot of her songs were partially inspired by him. I know ‘The One That Got Away’ and ‘Circle the Drain’ are partly about him, as well as Travis [McCoy of Gym Class Heroes]. But she was young and it was a time in her life she cherishes.” (Perry became a worldwide pop star in 2008 with her smash, “I Kissed a Girl,” and married Russell Brand in 2010. They finalized their divorce earlier this year.)

Adds the source, “They had good times. It’s really sad. She could never help him and couldn’t [let herself] go in that direction.”

On Wednesday, the body of 28-year-old Lewis was discovered in a driveway after the troubled actor fell or jumped from a rooftop following a fight with his landlady, Catherine Davis. (Authorities believe Lewis may have beaten Davis, 81, to death.)

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Sons of Anarchy creator Kurt Sutter took to his WhoSay page Thursday afternoon to admit that he wasn’t surprised at all to learn of Lewis’ violent, untimely passing.

“It was a tragic end for an extremely talented guy, who unfortunately had lost his way,” Sutter wrote. “I wish I could say that I was shocked by the events last night, but I was not.”

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