Question: Which season of American Idol featured a guest judge with the largest Twitter following in the world?

full_context: Document 1: American Idol: The fourteenth season premiered on January 7, 2015. Ryan Seacrest returned to host, while Jennifer Lopez, Keith Urban and Harry Connick, Jr. returned for their respective fourth, third and second seasons as judges. Eighth season runner-up Adam Lambert filled in for Urban during the New York City auditions. Randy Jackson did not return as the in-house mentor for this season.
Document 2: List of most-followed Twitter accounts: This list contains the top 50 accounts with the largest number of followers on the social media platform Twitter. As of 2 August 2018, the most followed person is American singer Katy Perry, with close to 107 million followers. Her account was the first to exceed 100 million followers, in June 2017.
Document 3: American Idol: Guest judges may occasionally be introduced. In season two, guest judges such as Lionel Richie and Robin Gibb were used, and in season three Donna Summer, Quentin Tarantino and some of the mentors also joined as judges to critique the performances in the final rounds. Guest judges were used in the audition rounds for seasons four, six, nine, and fourteen such as Gene Simmons and LL Cool J in season four, Jewel and Olivia Newton-John in season six, Shania Twain in season eight, Neil Patrick Harris, Avril Lavigne and Katy Perry in season nine, and season eight runner-up, Adam Lambert, in season fourteen.
Document 4: American Idol: In season eight, Latin Grammy Award-nominated singer–songwriter and record producer Kara DioGuardi was added as a fourth judge. She stayed for two seasons and left the show before season ten. Paula Abdul left the show before season nine after failing to agree terms with the show producers. Emmy Award-winning talk show host Ellen DeGeneres replaced Paula Abdul for that season, but left after just one season. On January 11, 2010, Simon Cowell announced that he was leaving the show to pursue introducing the American version of his show The X Factor to the USA for 2011. Jennifer Lopez and Steven Tyler joined the judging panel in season ten, but both left after two seasons. They were replaced by three new judges, Mariah Carey, Nicki Minaj and Keith Urban, who joined Randy Jackson in season 12. However both Carey and Minaj left after one season, and Randy Jackson also announced that he would depart the show after twelve seasons as a judge but would return as a mentor. Urban is the only judge from season 12 to return in season 13. He was joined by previous judge Jennifer Lopez and former mentor Harry Connick, Jr.. Lopez, Urban and Connick, Jr. all returned as judges for the show's fourteenth and fifteenth seasons.
Document 5: American Idol: Once in Hollywood, the contestants perform individually or in groups in a series of rounds. Until season ten, there were usually three rounds of eliminations in Hollywood. In the first round the contestants emerged in groups but performed individually. For the next round, the contestants put themselves in small groups and perform a song together. In the final round, the contestants perform solo with a song of their choice a cappella or accompanied by a band‍—‌depending on the season. In seasons two and three, contestants were also asked to write original lyrics or melody in an additional round after the first round. In season seven, the group round was eliminated and contestants may, after a first solo performance and on judges approval, skip a second solo round and move directly to the final Hollywood round. In season twelve, the executive producers split up the females and males and chose the members to form the groups in the group round.
Document 6: List of most-followed Instagram accounts: This list contains the top 10 accounts with the most followers on the social photo - sharing platform Instagram. As of December 2017, the most followed user is Instagram's own account, with over 230 million followers. Selena Gomez is the most followed individual, with over 132 million followers. Eight accounts have exceeded 100 million followers on the site.
Document 7: List of most-followed Instagram accounts: This list contains the top 25 accounts with the most followers on the social photo - sharing platform Instagram. As of February 2018, the most followed user is Instagram's own account, with over 232 million followers. Selena Gomez is the most followed individual, with over 133 million followers. Eight accounts have exceeded 100 million followers on the site.
Document 8: List of most-followed Twitter accounts: This list contains the top 50 accounts with the most followers on the social media platform Twitter. As of October 30, 2017, the most followed account is Katy Perry, with over 105 million followers. Her account was also the first to exceed 100 million followers.
Document 9: List of most-followed Instagram accounts: This list contains the top 25 accounts with the most followers on the social photo - sharing platform Instagram. As of July 2018, the most followed user is Instagram's own account, with over 241 million followers. Selena Gomez is the most followed individual, with over 138 million followers. Ten accounts have exceeded 100 million followers on the site.
Document 10: American Idol: With the exception of seasons one and two, the contestants in the semifinals onwards perform in front of a studio audience. They perform with a full band in the finals. From season four to season nine, the American Idol band was led by Rickey Minor; from season ten onwards, Ray Chew. Assistance may also be given by vocal coaches and song arrangers, such as Michael Orland and Debra Byrd to contestants behind the scene. Starting with season seven, contestants may perform with a musical instrument from the Hollywood rounds onwards. In the first nine seasons, performances were usually aired live on Tuesday nights, followed by the results shows on Wednesdays in the United States and Canada, but moved to Wednesdays and Thursdays in season ten.
Document 11: American Idol: American Idol employs a panel of judges who critique the contestants' performances. The original judges were record producer and music manager Randy Jackson, pop singer and choreographer Paula Abdul and music executive and manager Simon Cowell. The judging panel for the most recent season consisted of country singer Keith Urban, singer and actress Jennifer Lopez, and jazz singer Harry Connick, Jr. The show was originally hosted by radio personality Ryan Seacrest and comedian Brian Dunkleman, with Seacrest continuing on for the rest of the seasons.
Document 12: American Idol: The show had originally planned on having four judges following the Pop Idol format; however, only three judges had been found by the time of the audition round in the first season, namely Randy Jackson, Paula Abdul and Simon Cowell. A fourth judge, radio DJ Stryker, was originally chosen but he dropped out citing "image concerns". In the second season, New York radio personality Angie Martinez had been hired as a fourth judge but withdrew only after a few days of auditions due to not being comfortable with giving out criticism. The show decided to continue with the three judges format until season eight. All three original judges stayed on the judging panel for eight seasons.
Document 13: List of most-followed Instagram accounts: This list contains the top 25 accounts with the most followers on the social photo - sharing platform Instagram. As of May 2018, the most followed user is Instagram's own account, with over 235 million followers. Selena Gomez is the most followed individual, with over 137 million followers. Ten accounts have exceeded 100 million followers on the site.
Document 14: American Idol: Beginning in the tenth season[citation needed], permanent mentors were brought in during the live shows to help guide the contestants with their song choice and performance. Jimmy Iovine was the mentor in the tenth through twelfth seasons, former judge Randy Jackson was the mentor for the thirteenth season and Scott Borchetta was the mentor for the fourteenth and fifteenth season. The mentors regularly bring in guest mentors to aid them, including Akon, Alicia Keys, Lady Gaga, and current judge Harry Connick, Jr..
Document 15: List of most-followed Twitter accounts: This list contains the top 50 accounts with the largest number of followers on the social media platform Twitter. As of April 9, 2018, the most followed person is American singer Katy Perry, with over 108 million followers. Her account was the first to exceed 100 million followers, in June 2017.
ground_truth: season nine
sub_queries: who has the largest twitter following in the world Answer: Katy Perry
Which season of American Idol featured Katy Perry as a guest judge? Answer: season nine