What singer made appearances during Keith Urban's Ripcord World Tour who also the winner of the  fourth season of "American Idol"?
Ripcord World Tour 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.
American Idol (season 7) The seventh season of American Idol, the annual reality show and singing competition, began on January 15, 2008 and concluded on May 21, 2008. Ryan Seacrest continued to host the show with Simon Cowell, Paula Abdul, and Randy Jackson returning as judges. David Cook was announced the winner of the competition on May 21, 2008, defeating runner-up David Archuleta by a margin of roughly 12 million votes out of over 97 million, which was at that time the highest recorded vote total ever recorded in the show's history. The split was 56 % to 44 %.