Speaking to The Sun, the Fix You singer explained that RiRi features on LP track Princess of China, taken from their fifth studio album - due for release on 24th October.
When asked about the California King Bed hitmaker, Martin claimed: "She has such an amazing voice and it's so different to mine."
"When the vocal happened I thought 'Wow, you sound different' but I think that's also because she was singing a different song to what we are used to hearing from her and it is written by a bloke from Devon."
Gwyneth Paltrow's hubby then went on to confess that he was nervous about approaching Rihanna for the collaboration, stating: "The album is designed as a whole piece. It has boy and girl lead characters and top of our list for the girl part was Rihanna…"
Martin added: "But it took a while to pluck up the courage to ask her. We did a show in Las Vegas and I met her and said, 'Do you think there's any chance?' I was very Hugh Grant-like and spluttering about it."
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