Kristine says of their collaborative track Stronghold Of Angels: "This metal hymn is special to me - and Doro's unique voice takes it to an exceptional emotional level. Thank you, Doro, for staying with us, and for the late-night talks."

Vervain follows 2012 album Libertine, while Leaves' Eyes recently completed a European tour and play a 10th anniversary show in Belgium on October 18. Kristine joins Anneke van Giersbergen and Kari Rueslatten for a tour entitled The Sirens, including four European dates next month and four more in December.