The six-chair challenge took place on 1 and 2 September, at The SSE Arena, Wembley. 64 acts faced the six-chair challenge, with 16 in the Girls category, 16 in the Boys, 17 in the Overs, and 15 in the Groups. The challenge was broadcast on 4, 11 and 18 October. At the start of the challenge, the judges discovered which categories they would mentor: Ora was given the Girls, Grimshaw was given the Boys, Cowell was given Over 26s, and Fernandez-Versini was given the Groups. Tom Bleasby was originally put through, but it was reported on 12 October that he had withdrawn for personal reasons. On 15 October, it was announced that Mason Noise would replace Bleasby at Judges' Houses. On 20 October, it was revealed that all the groups would undergo name changes due to copyright reasons. The new names were revealed as 4th Impact (4th Power), Alien Uncovered (Alien), BEKLN Mile (BEKLN), Melody Stone (Silver Tone), New King Order (The First Kings) and Reggie 'n' Bollie (Menn On Point)  "The X Factor" resumed its usual Saturday and Sunday night slots for judges' houses, taking place over one weekend (24–25 October). Murs and Flack did not appear at judges' houses, but filmed from the studio. Judges' houses was planned to be broadcast fully live, and recorded back-to-back, but on 15 September, it was announced that this would not happen as it would cause logistical problems. Instead, the judges' houses performances were pre-recorded in the scheduled destinations, with all of the contestants who made it to that stage of the competition brought to London afterwards to watch the performances and find out if they had made it through to the live shows during a live broadcast. This was the only portion of judges' houses that was broadcast live. On 1 October, the guest judges for the judges' houses stage were revealed. Meghan Trainor assisted Ora in Los Angeles, Fernandez-Versini was joined by Jess Glynne in Rome, Mark Ronson helped Grimshaw in the Cotswolds, and Cowell's assistant was Louis Tomlinson, joining him in the Loire Valley, France. After being eliminated, Monica Michael was reinstated as a wildcard before the live shows. Key:  This year, there were seven weeks of live shows instead of the usual ten. ITV were contractually obliged to show all of Home Nation's Rugby World Cup games in October, some of which take place during "The X Factor‍"s Saturday night slot.