Katy Perry is ''devastated'' about the death of her ex-boyfriend Johnny Lewis.

The 'Firework' singer - who dated the 'Sons of Anarchy' star for 18 months until early 2007 - is believed to have been partly inspired by her former partner throughout her career, but knew she had to break up with him at the time because he was a troubled soul.

A source told USMagazine.com: ''She is devastated. She had to separate from him to get ahead and focus on her career. 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. But she was young and it was a time in her life she cherishes.''

Johnny is believed to have killed himself by leaping off his home after beating his 81-year-old landlady to death.

Police discovered the upstairs of the building had been ransacked and a cat had been killed.

A spokesperson for the Los Angeles Police Department said: ''It's a terrible tragedy as far as we're concerned and we're digging into the bottom of it.

''He appeared to have died from some type of fall, either from the stairway, or from the balcony, or from one of the roofs.

''The best we're piecing together now is that it appears that some type of altercation occurred inside of the house resulting in the death of the woman.''