The 37-year-old star - who is the subject of Katy's 2010 song 'The One That Got Away' - previously dated the pop star, but has revealed they ultimately decided they're better off as good friends.
Josh confessed: ''We did [date]. We were both very private and we realised we were better as friends and we've been very, very good friends to this day. She's the best.''
Katy, 33 - who is now dating actor Orlando Bloom - remained tight-lipped about the song for years, before revealing in 2017 that the track referred to her relationship with Josh.
And the American star has admitted the confession left him in a state of shock.
He told 'Watch What Happens Live With Andy Cohen': ''I was not expecting that. That was a double take and a spit of my coffee when I saw that.''
In fact, Josh - who is now dating actress Schuyler Helford - still has his doubts about whether the track is really about him.
He said: ''It's very sweet of her to say that, and then I listened to the lyrics of the song. And I'm like, 'I never owned a Mustang. I don't have a tattoo. Are you sure that's about me?'''
When he was encouraged by the show's host to reach out to Katy, Josh added: ''I think we're both very taken at the moment, but it's very sweet.''
Meanwhile, Orlando previously admitted that his romance with Katy was unexpected.
The Hollywood star explained: ''She's a remarkable human being, actually.
''I wouldn't have imagined anything happening. And, you know, when you get hit sideways you get hit sideways. You don't pick who you fall in love with.''
Just over two years since the release of her vibrant debut album, Anna Burch is back with her second full-length album: 'If You're Dreaming'.
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