Question: In what year did the singer of Barcelona die?

full_context: Document 1: Barcelona (Freddie Mercury and Montserrat Caballé song): "Barcelona" is a single released by Queen vocalist Freddie Mercury and operatic soprano Montserrat Caballé. A part of their collaborative album "Barcelona", it also appeared on Queen's "Greatest Hits III".
Document 2: Queen (band): Before forming Queen, Brian May and Roger Taylor had played together in a band named Smile. Freddie Mercury (then known by his birth name of Farrokh "Freddie" Bulsara) was a fan of Smile and encouraged them to experiment with more elaborate stage and recording techniques. Mercury joined the band in 1970, suggested "Queen" as a new band name, and adopted his familiar stage name. John Deacon was recruited prior to recording their eponymous debut album in 1973. Queen first charted in the UK with their second album, Queen II, in 1974, but it was the release of Sheer Heart Attack later that year and A Night at the Opera in 1975 which brought them international success. The latter featured "Bohemian Rhapsody", which stayed at number one in the UK for nine weeks and popularised the music video. Their 1977 album, News of the World, contained "We Will Rock You" and "We Are the Champions", which have become anthems at sporting events. By the early 1980s, Queen were one of the biggest stadium rock bands in the world. Their performance at 1985's Live Aid is ranked among the greatest in rock history by various music publications, with a 2005 industry poll ranking it the best. In 1991, Mercury died of bronchopneumonia, a complication of AIDS, and Deacon retired in 1997. Since then, May and Taylor have occasionally performed together, including with Paul Rodgers (2004–09) and with Adam Lambert (since 2011). In November 2014, Queen released a new album, Queen Forever, featuring vocals from the late Mercury.
Document 3: Queen (band): The band had a number of bass players during this period who did not fit with the band's chemistry. It was not until February 1971 that they settled on John Deacon and began to rehearse for their first album. They recorded four of their own songs, "Liar", "Keep Yourself Alive", "The Night Comes Down" and "Jesus", for a demo tape; no record companies were interested. It was also around this time Freddie changed his surname to "Mercury", inspired by the line "Mother Mercury, look what they've done to me" in the song "My Fairy King". On 2 July 1971, Queen played their first show in the classic line-up of Mercury, May, Taylor and Deacon at a Surrey college outside London.
Document 4: The Solo Collection: The Solo Collection is a box set detailing the solo career of Freddie Mercury; it includes the material Mercury recorded before joining up with Queen, up through the 1993 No More Brothers remixes. Mercury's singles and two studio albums are included, as well as a disc of instrumentals, numerous rare tracks, and a set of interviews conducted by David Wigg. Also included are two DVDs: a collection of music videos, and a documentary covering Mercury's life.
Document 5: Queen (band): Queen are a British rock band formed in London in 1970. Their classic line-up was Freddie Mercury (lead vocals and piano), Brian May (lead guitar and vocals), Roger Taylor (drums and vocals) and John Deacon (bass guitar). Their earliest works were influenced by progressive rock, hard rock and heavy metal, but the band gradually ventured into more conventional and radio-friendly works by incorporating further styles, such as arena rock and pop rock.
Document 6: Queen (band): After fans noticed Mercury's increasingly gaunt appearance in 1988, rumours began to spread that Mercury was suffering from AIDS. Mercury flatly denied this, insisting he was merely "exhausted" and too busy to provide interviews. The band decided to continue making albums, starting with The Miracle in 1989 and continuing with Innuendo in 1991. Despite his deteriorating health, the lead singer continued to contribute. For the last two albums made while Mercury was still alive, the band credited all songs to Queen, rather than specific members of the group, freeing them of internal conflict and differences. In 1990, Queen ended their contract with Capitol and signed with Disney's Hollywood Records, which has since remained the group's music catalogue owner in the United States and Canada. That same year, Mercury made his final public appearance when he joined the rest of Queen to collect the Brit Award for Outstanding Contribution to British Music.
Document 7: Queen (band): On 25 and 26 April, May and Taylor appeared on the eleventh series of American Idol at the Nokia Theatre, Los Angeles, performing a Queen medley with the six finalists on the first show, and the following day performed "Somebody to Love" with the 'Queen Extravaganza' band. Queen were scheduled to headline Sonisphere at Knebworth on 7 July 2012 with Adam Lambert before the festival was cancelled. Queen's final concert with Freddie Mercury was in Knebworth in 1986. Brian May commented, "It's a worthy challenge for us, and I'm sure Adam would meet with Freddie's approval." Queen expressed disappointment at the cancellation and released a statement to the effect that they were looking to find another venue. It was later announced that Queen + Adam Lambert would play two shows at the Hammersmith Apollo, London on 11 and 12 July 2012. Both shows sold out within 24 hours of tickets going on open sale. A third London date was scheduled for 14 July. On 30 June, Queen + Lambert performed in Kiev, Ukraine at a joint concert with Elton John for the Elena Pinchuk ANTIAIDS Foundation. Queen also performed with Lambert on 3 July 2012 at Moscow's Olympic Stadium, and on 7 July 2012 at the Municipal Stadium in Wroclaw, Poland.
Document 8: The Freddie Mercury Album: The Freddie Mercury Album is a posthumous solo project with material from Queen frontman and vocalist Freddie Mercury released in 1992, to observe the anniversary of his death. The album is mainly made up of remixes from his past releases, as well as the original versions of "Barcelona", "Love Kills", "Exercises in Free Love", and "The Great Pretender". A week later, The Great Pretender, its US counterpart, was released.
Document 9: Queen (band): Innuendo was released in early 1991 with an eponymous number 1 UK hit and other charting singles including, "The Show Must Go On". Mercury was increasingly ill and could barely walk when the band recorded "The Show Must Go On" in 1990. Because of this, May had concerns about whether he was physically capable of singing it. Recalling Mercury's successful performance May states; "he went in and killed it, completely lacerated that vocal". The rest of the band were ready to record when Mercury felt able to come in to the studio, for an hour or two at a time. May says of Mercury: “He just kept saying. 'Write me more. Write me stuff. I want to just sing this and do it and when I am gone you can finish it off.’ He had no fear, really.” The band's second greatest hits compilation, Greatest Hits II, followed in October 1991, which is the eighth best-selling album of all time in the UK and has sold 16 million copies worldwide.
Document 10: Queen (band): Brian May and Roger Taylor performed together at several award ceremonies and charity concerts, sharing vocals with various guest singers. During this time, they were billed as Queen + followed by the guest singer's name. In 1998, the duo appeared at Luciano Pavarotti's benefit concert with May performing "Too Much Love Will Kill You" with Pavarotti, later playing "Radio Ga Ga", "We Will Rock You", and "We Are the Champions" with Zucchero. They again attended and performed at Pavarotti's benefit concert in Modena, Italy in May 2003. Several of the guest singers recorded new versions of Queen's hits under the Queen + name, such as Robbie Williams providing vocals for "We Are the Champions" for the soundtrack of A Knight's Tale (2001).
Document 11: Queen (band): In 1999, a Greatest Hits III album was released. This featured, among others, "Queen + Wyclef Jean" on a rap version of "Another One Bites the Dust". A live version of "Somebody to Love" by George Michael and a live version of "The Show Must Go On" with Elton John were also featured in the album. By this point, Queen's vast amount of record sales made them the second best selling artist in the UK of all time, behind the Beatles. In 2002, Queen were awarded the 2,207th star on the Hollywood Walk of Fame, which is located at 6358 Hollywood Blvd. On 29 November 2003, May and Taylor performed at the 46664 Concert hosted by Nelson Mandela at Green Point Stadium, Cape Town, to raise awareness of the spread of HIV/AIDS in South Africa. May and Taylor spent time at Mandela's home, discussing how Africa's problems might be approached, and two years later the band was made ambassadors for the 46664 cause.
Document 12: Queen (band): Between 2005 and 2006, Queen + Paul Rodgers embarked on a world tour, which was the first time Queen toured since their last tour with Freddie Mercury in 1986. The band's drummer Roger Taylor commented; "We never thought we would tour again, Paul [Rodgers] came along by chance and we seemed to have a chemistry. Paul is just such a great singer. He's not trying to be Freddie." The first leg was in Europe, the second in Japan, and the third in the US in 2006. Queen received the inaugural VH1 Rock Honors at the Mandalay Bay Events Center in Las Vegas, Nevada, on 25 May 2006. The Foo Fighters paid homage to the band in performing "Tie Your Mother Down" to open the ceremony before being joined on stage by May, Taylor, and Paul Rodgers, who played a selection of Queen hits.
Document 13: Queen (band): At the end of 2004, May and Taylor announced that they would reunite and return to touring in 2005 with Paul Rodgers (founder and former lead singer of Free and Bad Company). Brian May's website also stated that Rodgers would be "featured with" Queen as "Queen + Paul Rodgers", not replacing Mercury. The retired John Deacon would not be participating. In November 2004, Queen were among the inaugural inductees into the UK Music Hall of Fame, and the award ceremony was the first event at which Rodgers joined May and Taylor as vocalist.
Document 14: Queen (band): After working on various solo projects during 1988 (including Mercury's collaboration with Montserrat Caballé, Barcelona), the band released The Miracle in 1989. The album continued the direction of A Kind of Magic, using a pop-rock sound mixed with a few heavy numbers. It spawned the European hits "I Want It All", "Breakthru", "The Invisible Man", "Scandal", and "The Miracle". The Miracle also began a change in direction of Queen's songwriting philosophy. Since the band's beginning, nearly all songs had been written by and credited to a single member, with other members adding minimally. With The Miracle, the band's songwriting became more collaborative, and they vowed to credit the final product only to Queen as a group.
Document 15: Queen (band): In 1997, Queen returned to the studio to record "No-One but You (Only the Good Die Young)", a song dedicated to Mercury and all those that die too soon. It was released as a bonus track on the Queen Rocks compilation album later that year. In January 1997, Queen performed "The Show Must Go On" live with Elton John and the Béjart Ballet in Paris on a night Mercury was remembered, and it marked the last performance and public appearance of John Deacon, who chose to retire. The Paris concert was only the second time Queen had played live since Mercury's death, prompting Elton John to urge them to perform again.
ground_truth: 1991
sub_queries: Barcelona >> performer Answer: Freddie Mercury
In what year did Freddie Mercury die? Answer: 1991