Question: What singer made appearances during Keith Urban's Ripcord World Tour who also the winner of the  fourth season of "American Idol"?
Context: An American Idol Christmas (also titled A Very Idol Christmas in Canada) is a Christmas television special for the television shows "American Idol", "American Juniors" and "Canadian Idol", but focused mostly on "American Idol"– the Canadian winner Ryan Malcolm was edited out in the American release, due to legal reasons.  The special was broadcast on the Fox television network in the United States and CTV in Canada.  It was first broadcast on November 25, 2003 in the United States.  It featured some of the top finalists of American Idol's first season (Kelly Clarkson, Tamyra Gray, Christina Christian) and second season (Ruben Studdard, Clay Aiken, Kimberley Locke); "Canadian Idol" winner Ryan Malcolm (not shown in American version due to the upcoming World Idol); and the American Juniors.  Since the episode was not a competition, none of the judges appeared because they were working on the next season's contestants.  It was directed by Bruce Gowers, produced by 19 Entertainment, Fremantle Media North America, Cécile Frot-Coutaz, Simon Fuller, David Goffin, Nigel Lythgoe and Ken Warwick. The fifteenth season of "American Idol", also branded as American Idol: The Farewell Season, premiered on the Fox television network on January 6, 2016.  Ryan Seacrest continued as the show's host, while Jennifer Lopez, Keith Urban, and Harry Connick, Jr. returned as judges.  This season was four to six weeks shorter than seasons 2 through 14.  On April 7, Trent Harmon was announced as the season's winner and La'Porsha Renae was the runner-up.  Harmon was the third consecutive winner to never be in the bottom two or three, and the eighth male winner in nine years. The Ripcord World Tour (stylized as the ripCORD World Tour) was the eleventh concert tour by Australian singer Keith Urban.  The tour was in support of his tenth studio album "Ripcord" (2016).  The tour began on 2 June 2016 in Bonner Springs, Kansas and concluded on 17 December 2016 with two shows in Brisbane, Australia.  Brett Eldredge, Maren Morris and Dallas Smith were supporting acts for Urban in North America.  The Oceania leg of the tour was co-headlined with American singer Carrie Underwood, with Buchanan as opening act. Anoop Manoj Desai (born December 20, 1986) is an American singer-songwriter best known for his time as a contestant on the eighth season of "American Idol".  Motivated by the death of his friend Eve Carson, Desai auditioned for "American Idol".  Desai made "American Idol" history by being the first ever 13th finalist on "American Idol".  Favored to win by celebrities including Ellen DeGeneres and Keith Urban, Desai achieved a sixth-place finish, becoming the second Indian American to advance to the final stages of "American Idol". Carrie Marie Underwood (born March 10, 1983) is an American singer, songwriter, and actress.  She rose to fame as the winner of the fourth season of "American Idol" in 2005.  Her debut album, "Some Hearts", was released in 2005.  Bolstered by the huge crossover success of the singles "Jesus, Take the Wheel" and "Before He Cheats", it became the best-selling solo female debut album in country music history, the fastest-selling debut country album in Nielsen SoundScan history and the best-selling country album of the last 14 years.  Underwood won three Grammy Awards for the album, including Best New Artist. The thirteenth season of "American Idol", styled as American Idol XIII, premiered on the Fox television network on January 15, 2014.  Ryan Seacrest returned as host for his thirteenth season.  Keith Urban was the only judge from the twelfth season to return.  Former judge Jennifer Lopez, who returned after one season absence, and Harry Connick, Jr. joined the judging panel following the departures of Mariah Carey, Nicki Minaj and Randy Jackson. The fourteenth season of "American Idol", also known as American Idol XIV, premiered on the Fox television network on January 7, 2015.  Ryan Seacrest continues his role as host, while Jennifer Lopez, Keith Urban and Harry Connick, Jr. returned for their respective fourth, third and second times as judges.  Randy Jackson stepped down as mentor, being replaced by Scott Borchetta.  Long-time sponsor Coca-Cola ended its relationship with the show.  This was the fourth season to have an all-male finale and the third season where the final two contestants had never been in the bottom group prior to the finale. NZ Idol, more commonly known as New Zealand Idol, was the New Zealand version of the Idol series originated as the hit British TV series "Pop Idol".  New Zealand first saw the "Idol" format when TV2 aired "American Idol 2", which garnered impressive ratings.  After "Australian Idol" also received good ratings in New Zealand, TVNZ decided to order the first season of "NZ Idol", which was broadcast on TV2.  After the third season in 2006, TVNZ made a decision not to fund or broadcast a fourth season, thus placing "New Zealand Idol" on indefinite hiatus, with no plans to run a fourth season. "Falling" is the debut single by "American Idol" season fifteen winner Trent Harmon and is also his coronation song from the contest.  It was co-written by singer songwriter and "American Idol" judge Keith Urban with Dallas Davidson and Brett James.  This song also failed to chart on the Billboard Hot 100 thus making it the second and the final American Idol coronation single to do so. Harold Elwin "Bo" Bice, Jr. (born November 1, 1975) is an American singer and musician who was the runner-up against Carrie Underwood in the fourth season of "American Idol".  Prior to auditioning for "American Idol", Bice released a solo album as well as a few albums with his bands while performing in the night club circuit.  In 2005, Bice charted at number two on the "Billboard" Hot 100 with a rendition of "Inside Your Heaven" from "American Idol".  He released the album "The Real Thing" after "American Idol" to minor success before being dropped by RCA Records.  He started his own record label Sugar Money and subsequently released two more albums, "See the Light" and "3".  As of 2014, he is also the lead singer of the touring version of Blood, Sweat & Tears.
Answer: Carrie Underwood