Boyzone singer Stephen Gately has died suddenly at the age of 33 while on holiday in Majorca.
Spanish police said there were no signs of suspicious circumstances, but the cause of death is not yet known.
Gately was on holiday with his long-term partner Andy Cowles. His bandmates said they were "completely devastated" and are now travelling to Majorca.
Boyzone manager Louis Walsh has pulled out of Sunday's edition of ITV1's X Factor in the wake of Gately's death.
The four remaining members of Boyzone described Gately as "our friend and brother".
"We have shared such wonderful times together over the years and were all looking forward to sharing many more," a statement said.
"Stephen was a beautiful person in both body and spirit. He lit up our lives and those of the many friends he had all over the world. Our love and sympathy go out to Andrew and Stephen's family. We love you and will miss you forever."
The Irish band had six UK number one hits in the 1990s and reformed in 2007.
Singer Ronan Keating is on his way back from the US and will join the rest of the group in Majorca.
Police said they were called to a house near Port d'Andratx on the western tip of the island on Saturday afternoon.
"At the moment it is not known how he died," the police spokesman said. "There are no signs of suspicious circumstances."
Louis Walsh's spokeswoman confirmed that the manager would not go ahead with his X Factor appearance.
His spokeswoman said: "He thanks you all for the messages of support at this sad time."
Walsh earlier told the News of the World newspaper: "We're all absolutely devastated.
"I'm in complete shock. I was only with him on Monday at an awards ceremony. We don't know much about what's happened yet.
"I only heard after The X Factor and we will rally around each other this week. He was a great man."
Bertie Ahern, former Irish Taoiseach, described Gately as a personal friend and his death as a "huge, huge tragedy" for Irish music and culture.
Singer Sir Elton John said: "David and I are stunned by this tragedy. Stephen was the kindest, gentlest soul.
"We send our love and condolences to his partner Andy and to all his friends everywhere."
Fellow Irish boy band Westlife described Gately as a "friendly, positive spirit and a passionate performer...
"Our thoughts are with Andy and the rest of his family, his friends, his legions of fans and of course his bandmates... who will be devastated at the loss of a truly beautiful person."
Writing on the micro-blogging website Twitter, broadcaster Stephen Fry said: "Just heard the very sad news about dear Stephen Gately.
"What a dreadful shock. He was loveable and sweet-natured and will be hugely missed."
Music journalist Paul Gambaccini said: "It's sad on a personal level and a professional level."
Boyzone sold more singles than Take That in the 1990s, he said, and had 16 Top 5 singles.
A year before Boyzone split, Gately revealed that he was gay and had a boyfriend.
He later held a private civil partnership ceremony in London in 2006.
After Boyzone, Gately continued his career as a solo artist, but was dropped by Polydor in 2001 after three top 20 singles.
He enjoyed further success performing in musicals, including Joseph and the Amazing Technicolor Dreamcoat in 2003-04.
Gately also appeared in 2007 on ITV1's reality series Dancing on Ice, and was voted Hero of 1999 at the Smash Hits Poll Winners' Party.
His last message on Twitter, posted on 6 October, said: "Still busy - lots going on. Focussing on finishing my book next so may be quiet here."