Answer by taking a quote from the following article:

Symphony X is an American progressive metal band from Middletown, New Jersey. Founded in 1994, the band consists of guitarist Michael Romeo, keyboardist Michael Pinnella, drummer Jason Rullo, lead vocalist Russell Allen and bassist Michael Lepond. They achieved some commercial success with the 2007 album Paradise Lost and the 2011 album Iconoclast, which reached number 76 on the Billboard 200. Romeo explained the band's name in a 2008 interview; "So, you know, the music we were coming up with had the keyboard thing and the guitar, and some classical elements, so the word 'Symphony' came up and, so the dramatic thing, you know?

The band is working on releasing a second fan club CD. Michael Romeo said it will be another collection of demo tunes and other rare material, and may also include a bit of content created just for the release, along the lines of MJR's Star Wars tune on the first fan club CD, Rarities and Demos, which has since sold out of its first pressing. SXW, the band's revamped fan club, has relaunched and is now active.  The band began recording the drum tracks for the new album on September 9, 2014, and planned to release the complete recording by the spring of 2015. Michael Lepond stated they had ten songs written and that the album would contain either nine or all ten of them. He also stated all lyrics and instrumental tracks were composed and ready to be brought together, and that the album would be less heavy than Iconoclast: "If I had to compare, I would say that it's a combination of The Odyssey and Paradise Lost -- something in there. It has a lot of classic Symphony X elements in it, which I think a lot of our fans were missing for a few years. So I think our fans will really like this one. It really just focuses on solid songwriting."  As of December 11, 2014, recording of the drums, lead vocals, rhythm guitar, and bass were complete. With the keyboards, guitar solos, background vocals, and some miscellaneous odds and ends being done in the coming weeks. On April 10, 2015 the band announced the mixing and mastering of the new album was complete. On May 18, 2015, the band announced the title of the album would be titled Underworld, and a release date of July 24, 2015. The first single from the album, "Nevermore", premiered on May 22, 2015. The band released the second single, "Without You", on June 19, 2015, and was made available for digital download.  According to singer Russell Allen, the band entered a short hiatus during 2017 in which they did not perform, due in part to his commitment to Adrenaline Mob, although it was announced during a January 2018 interview with Metal Nation that the band had plans to get together in the following months and begin writing a follow up to Underworld. On July 14, 2017, Adrenaline Mob was involved in a serious vehicular accident, which resulted in severe injuries for Allen and two deaths.

When was the album released?
a release date of July 24, 2015.