From the official website of the Norvegian band:
"Kristian (Gundersen) has decided to part ways with Sirenia in order to concentrate on his other projects. We would like to wish him all the best for the future and extend our gratitude for almost 4 years of rock n' roll cooperation. Goth bless you Kris! Currently the band is auditioning new guitarplayers".

http://www.sirenia.no/

Band profile:

Sirenia