His wife Dwina, brother Barry, 65, daughter Melissa, 37, and sons Spencer, 39, and Robin-John, 29, were at his bedside at a private hospital in Chelsea, West London.

A family friend told the newspaper: 'Our prayers are with Robin. he has kept so positive and always believed he could beat this.

Sadly, it looks like he has developed pneumonia, which is very bad in his situation.

'If there is anyone you would put money on pulling through such a dire situation, it would be Robin because he is a fighter. But this is a battle he will struggle to win.'

Robin revealed his battle with cancer in October 2010.

He had emergency surgery to treat a blocked bowel, before a further operation to treat a twisted bowel. Colon cancer was then discovered and it spread to his liver.

His twin brother Maurice died of complications resulting from a twisted intestine in 2003, aged 53.

Height of their fame: Robin, right and his late twin brother Maurice, left, and older brother Barry performing in 1979

His brother's arrival this week comes after his nephew - Robin's son - RJ described the overwhelming moment the family learned that the Bee Gees star was in remission from cancer.

Robin famously appeared on the Alan Titchmarsh Show looking pale and gaunt and has cancelled a handful of appearance over the past two years because of his health.

Barry Gibb earlier this week jetted into the UK from Tennessee in the U.S. to join other members of the family.

However, this isn't the first time that Robin's fans have been left worried as the singer re-entered hospital back in February.

Robin was admitted into a London clinic as part of his treatment and rehabilitation.

At the time a family source told The Sun: 'We feared the worst. But doctors have said they are astounded at his response to treatment.'

The 29-year-old, full name Robin-John, revealed that he was sitting next to his famous father in his hospital bed when the doctor told them the happy news.

'I leant over the bed and I kissed him on the forehead and just said, "I love you",' RJ told the Mirror.

'Then we sat together for ages, just taking it all in and being together without saying anything.
'It was the best news we could have hoped for. It was the most beautiful feeling and instantly life was so much better.'

True love: Robin and his wife Dwina at their Oxfordshire home in 2010

Despite being admitted to hospital last week for further intestinal surgery, the singer had been given the all clear.

A statement released on the singer's behalf said: 'On Sunday 25 March, Robin Gibb underwent further intestinal surgery.

'He is currently recovering in hospital and therefore, for the time being, all existing commitments prior to the Titanic Requiem concert, have had to be cancelled.'

Robin and RJ had composed the music for the Royal Philharmonic performance at Westminster Central Hall next week.

Brotherly love: Robin's sibling Barry arrived in the UK this week to be by his brother's side

In February he had talked about feeling 'fantastic' following his treatment and said he had begun to put on weight after looking increasingly gaunt.

At first his illness was thought to have been due to the hereditary intestinal condition which led to the death of his twin brother.

Speaking about his cancer, last month he said: 'The prognosis is that it's almost gone and I feel fantastic and really from now on it's just what they could describe as a "mopping-up" operation.'

In an interview earlier this month, Gibb pondered whether his illness is 'karma' for the fame and fortune.he has enjoyed.

‘I sometimes wonder if all the tragedies my family has suffered, like Andy and Maurice dying so young and everything that’s happened to me recently, is a kind of karmic price we are paying for all the fame and fortune we’ve had.

‘But we’ve worked hard for everything we’ve achieved.’

A picture of health: Robin performing at The London Palladium in February