Il Divo singer Carlos Marin has died after becoming unwell during the group’s UK Christmas tour.

The quartet had postponed the rest of their British tour dates by a year earlier this month due to an unspecified illness.  On December 16th the outfit disclosed that Marin had been admitted to a hospital.

The cause of death has not yet been confirmed. Some reports in the Spanish media suggested the singer was intubated after being admitted to an intensive care unit in Manchester.

Several publications have branded the baritone's passing as a “COVID death”, though no official source has yet corroborated the report.

Il Divo announced Marin's passing on Twitter last night (December 19).

"It is with heavy hearts that we are letting you know that our friend and partner, Carlos Marin, has passed away. He will be missed by his friends, family and fans. There wiIl never be another voice or spirit like Carlos."

It is with heavy hearts that we are letting you know that our friend and partner, Carlos Marin, has passed away. He will be missed by his friends, family and fans. There wiIl never be another voice or spirit like Carlos. pic.twitter.com/uyRFjXADF6

— Il Divo (@ildivoofficial) December 19, 2021

"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. With Love -- David, Sebastien, and Urs" the band added.

The multi-national classical crossover group was founded by Simon Cowell in 2003. Marin joined up with fellow tenors Urs Buhler and David Miller and pop singer Sebastien Izambard.

The group's 2004 self-titled album Il Divo skyrocketed to number one in the UK, Canada, Australia, and the Netherlands. Through their 17-year long career the outfit undertook six world tours and sold over 30 million records.

Tributes to Marin poured in on social media, with Simon Cowell tweeting: "I am finding this so difficult to put into words how I feel right now.

"I am devastated Carlos Marin has passed away. He loved life. He loved performing and always had so much appreciation towards the fans who supported the group from day 1. Rest in peace Carlos. I will miss you."

I am finding this so difficult to put into words how I feel right now. I am devastated Carlos Marin has passed away. He loved life. He loved performing and always had so much appreciation towards the fans who supported the group from day 1. Rest in peace Carlos. I will miss you.

— Simon Cowell (@SimonCowell) December 20, 2021

Strictly Come Dancing judge Bruno Tonioli  wrote: "We had the best time putting together the first Il Divo performance 17 years ago great voice great man a true passionate Spirit with wicked sense of humor we will miss you so sad.”

Devastated @ildivoofficial @carlosmarin_ passed away
We had the best time putting together the first @ildivoofficial performance 17 yeas ago great voice great man a true passionate Spirit with wicked sense of humor we will miss you so sad❤️B

— Bruno Tonioli (@BrunoTonioli) December 19, 2021

UK-based musical theatre group Collabro and English singer Michael Ball also paid tribute to the Spanish baritone.

We are so sorry to hear of the passing of Carlos Marín. His voice and stage presence were spectacular and he was as brilliant off stage as he was whilst performing. Sending love to @ildivoofficial during this very difficult time. pic.twitter.com/dLEUCgoQvC

— COLLABRO (@Collabro) December 19, 2021

Unbelievably sad to hear of the the passing of the lovely @carlosmarin_ a charismatic, charming and hugely talented man. A total one off. Sending my love to all @ildivoofficial family and friends. #RIPCarlosMarin

— Michael Ball OBE (@mrmichaelball) December 20, 2021

Outside of Il Divo, Marin was a respected stage performer, taking on roles in musicals such as Les Miserables, Grease, and Beauty And The Beast.