Answer by taking a quote from the following article:

The Bee Gees were a pop music group formed in 1958. Their lineup consisted of brothers Barry, Robin, and Maurice Gibb. The trio were successful for most of their decades of recording music, but they had two distinct periods of exceptional success: as a popular music act in the late 1960s and early 1970s, and as prominent performers of the disco music era in the mid-to-late 1970s. The group sang recognisable three-part tight harmonies; Robin's clear vibrato lead vocals were a hallmark of their earlier hits, while Barry's R&B falsetto became their signature sound during the mid-to-late 1970s and 1980s.

In an interview with Easy Mix radio host Tim Roxborough on 1 September 2009, Barry's 63rd birthday, Barry commented on future tours saying that "they will be back"; but in an agreement with Warner/Rhino they would not make an announcement at that time. On 7 September 2009, Robin disclosed to Jonathan Agnew that he had been in touch with Barry and that they had agreed that the Bee Gees would re-form and "perform again".  Barry and Robin performed on the BBC's Strictly Come Dancing on 31 October 2009 and appeared on ABC-TV's Dancing with the Stars on 17 November 2009. On 15 March 2010, Barry and Robin inducted the Swedish group ABBA into the Rock and Roll Hall of Fame. On 26 May 2010, the two made a surprise appearance on the ninth-season finale of American Idol.  On 20 November 2011 it was announced that Robin Gibb, at 61 years old, had been diagnosed with liver cancer, a condition he had become aware of several months earlier. He had become noticeably thinner in previous months and had to cancel several appearances due to issues with severe abdominal pain.  On 13 February 2012, Robin joined British military trio the Soldiers for the Coming Home charity concert at the London Palladium, in support of injured servicemen. It was his first public appearance for almost five months and his final.  On 14 April 2012, it was reported that Robin had contracted pneumonia in a Chelsea hospital and was in a coma. Although he came out of his coma on 20 April 2012, his condition deteriorated rapidly, and he died on 20 May 2012 of liver and kidney failure. With Robin's death, Barry became the last surviving Gibb brother, and the Bee Gees dissolved as a musical group.

When was Robin's death?
20 May 2012