On August 30, the band announced that the lead single Paradise (What About Us?) would be released as an EP, which is also set to feature 3 tracks from the upcoming album in their demo form, being them "Let Us Burn", "Silver Moonlight" and "Dog Days". Upon making this announcement, den Adel said: "By releasing these demos 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 demo versions are far from their final sound on the album, but will give you a hint of what we’re working on. It will be fascinating to hear how the end result will sound like, once the album is released.". After announcing that the lead single would contain a guest musician, on September 13 the band officially announced that Tarja Turunen was set to appear as a special vocalist on the title song. The EP was released on September 27. On October 25 and 26, den Adel and Westerholt presented an unknown number of songs of the upcoming album to the press. The second promotional single, Dangerous, was released on December 20 and features ex-Killswitch Engage singer Howard Jones. Hydra was finally released on January 31, 2014, in mainland Europe and on February 4 on North America and United Kingdom, and was met with critical and commercial success. In the Netherlands, "Hydra" marked the band's return to the first position on the charts since the release of "The Heart of Everything" in 2007, also reaching the first spot on the Czech Republic album charts, making it their first number-one album outside the Netherlands. The band had their first album on a top 10 position in the UK Albums Chart, debuting at six and the first top 20 position on the US "Billboard" 200, debuting at the number 16.