Carlos Marín, a singer in the group Il Divo, has died aged 53 during the band's Christmas tour in the United Kingdom.
Just a few days ago, his bandmates revealed Marín was in hospital, having cancelled several of their shows due to unexplained illness.
They announced his death "with heavy hearts" in a statement on social media.
"He will be missed by his friends, family and fans. There wiIl never be another voice or spirit like Carlos," they said.
"For 17 years the four of us have been on this incredible journey of Il Divo together, and we will miss our dear friend. We hope and pray that his beautiful soul will rest in peace."
Il Divo began its Christmas tour across the UK on December 1, but halfway through several shows were postponed "due to illness".
The band did not disclose it was Marín who was unwell until after Spanish newspaper El Espanol reported he was in an induced coma at a hospital in Manchester.
The nature of Marín's illness was not publicly announced.
Marín, along with Urs Bühler, Sébastien Izambard and David Miller joined Il Divo in 2003. This year they celebrated 17 years together.
The multi-national quartet was formed by music producer Simon Cowell, and has enjoyed worldwide acclaim.
The group, which performed operatic pop and classical crossover, has had six world tours and sold over 30 million records.
Marín was born in Germany in 1968 and lived in Madrid in Spain from the age of 12.
He performed in a number of operas and musicals before joining Il Divo.
The acclaimed baritone also performed solo concerts from 2011, while remaining a member of the group.
Together, Il Divo performed for high-profile figures including former US presidents George Bush, Bill Clinton and Barack Obama, as well as Queen Elizabeth II.
They also collaborated with Celine Dion, Tony Braxton, Kristin Chenoweth and Michael Ball.
