The 'It Wasn't Me' reggae star and the rock legend surprised the world with the news they are to release LP '44/876', which stands for the area codes for the UK and Jamaica.
And The Police star was stunned by the 49-year-old musician's ''personal'' process.
In an interview with The Sun newspaper, Sting confessed: ''We have very different creative processes,'' he says. ''I'm very private and I don't reveal anything until I'm ready, it's anxiety I think.
''But this one (glances at Shaggy) is such a spontaneous creator.
''He can make a song on the spot, in public, and doesn't mind making a mistake.
''He just does it!
''He invited me into that world.
''I was slightly uncomfortable but once we stood side-by-side at a microphone, I got into it.''
The 'Every Breath You Take' hitmaker was joined on stage by Shaggy at his solo gig in Antwerp, Berlin in 2004, so the album is the result of their meeting 14 years ago.
Sting previously revealed that he and the Jamaican-American rapper got together last year ''to jam and create music that reflects their mutual love of Jamaica, its music, people and culture'' and, as a result of their time in the studio, they've come up with some ''Caribbean-flavoured songs.''
Speaking about how they have ''a lot in common'', he added: ''We have a lot in common. We're both married to very strong women. We both come from small islands that used to belong to the queen. And we like each other. We like each other's voices and music and vibe. We're like kindred spirits.''
'44/876' is released on April 20.
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