In 2003 Tuomas released an album called Fallen with For My Pain. This project has since been put on hold again. He also worked with metal band Kotiteollisuus, playing on the album Helvetistä itään and later the album 7.
2004 was the year of US breakthrough. Once was released and the band toured places they had never been before. Also there was a DVD made of the final concert, End of an Era. It was this concert where the famous letter was given to Tarja about her dismissal from the band.
After Once, Tuomas fell into what he calls his “dark period”, a time in his life filled with depression. He could not open tabloids without reading something about himself or Nightwish.