But in the clip below, two lead-singer microphones are seen, followed by two pairs of ladies' shoes � leading fans to speculate that Sharon den Adel has recorded a duet with another female vocalist.

The band haven't confirmed or denied. But they do say: "We want to invite you in our home studio and show how we capture song ideas at an early stage of creating a new album.

"These demos are far from their final sound, but they'll give you a hint of what we're working on. It will be fascinating to hear the end result.