Katy Perry has said she had a "long courtship" with John Mayer before their relationship really took off.
The singers have had an on-off relationship following Katy's divorce from Russell Brand.
Katy, 29, told Entertainment Weekly: "We had a long courtship before anything was (public), just writing letters to each other."
Their relationship was the inspiration for Katy's track Legendary Lovers.
She said: "I actually wrote it in an email one time, and after I wrote it I looked. .. and seeing 'legendary lovers', it sounded so nice.
"Some things float into my mind, and I process them, and (then) I make songs about them."
The romance between Roar singer Katy and 36-year-old John, who previously dated Taylor Swift, Jennifer Aniston, and Jessica Simpson, came soon after Katy finalised her divorce Russell in 2012.