The 62-year-old founding member of disco-era hit machine the Bee Gees, said in February that he had made a "spectacular" recovery from cancer, but had intestinal surgery last month. He was hospitalized late last year for stomach and colon problems.

Robin Gibb composed the symphonic "Titanic Requiem" with his son, Robin-John Gibb, and had been scheduled to perform a new song, "Don't Cry Alone," during the concert at Westminster Central Hall on Tuesday.

Robin-John confirmed that his father was undergoing treatment in a London hospital.

"Of course these are all the periphery problems that occur when you have an illness like that. It's not always the cancer that will get you, and he has to always be treated and always keep good scrutiny on his health," he told Reuters Television.

"Sadly that's the way it is, and tonight he would love to be here and we're really at a loss because we really wanted him to see this and be able to see our baby come to fruition."

Robin Gibb's brother and fellow Bee Gee Barry Gibb also was due to attend the concert but did not show. British newspapers have reported that he had flown to London to be at his brother's hospital bedside.

"I don't think there'll ever be a time in the future where he is not in and out of hospital because you have to keep constant scrutiny on these things. But if anyone can carry on it's him - he's a very strong individual," Robin-John said.

"The Titanic Requiem," performed by the Royal Philharmonic Orchestra, is being released to mark the 100th anniversary of the sinking of the luxury liner on April 15, 1912.

"Today he wanted to have the requiem fed into his room but now that we're going live feed on the Internet, he can easily get a good peek at it," Robin-John Gibb said.

"A lot of this requiem was written in the hospital bedrooms with my father because, of course, he was diagnosed when we were in the middle of composing."

Media speculation about Gibb's health was sparked in recent months by his gaunt and frail appearance. But the singer said in February that a growth in his colon had "almost gone" and he was feeling "fantastic."

The Bee Gees enjoyed a string of disco era hits including "Stayin' Alive."

(Reporting by Reuters Television; Writing by Elaine Lies; Editing by Bob Tourtellotte)

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