Sia Furler
Sia Furler performed on American Idol and also mentored the finalistsRick Kern/Getty Images for Samsung

American Idol's final four contestants were announced on the 24 March episode and as if making it this far in the singing competition wasn't awesome enough, the finalists also got to work "face to face" with Sia when she mentored. La'Porsha Renae, Dalton Rapattoni, Trent Harmon and Mackenzie Bourg spent the night performing two songs – a rock number along with a track of Sia's. Sonika Vaid who had the least number of votes was sent home before she got the chance to perform though.

Sia performed her new single Cheap Thrills and also mentored the finalists, giving them a chance to see her without her trademark face-covering wig. Prior to the meeting, contestant La'Porsha Renae told HollywoodLife: "I am so excited to meet Sia and get the chance to do one of her songs. All of us are excited to meet her. I hope that she allows me to see her face. I need to see the behind the scenes, I won't take pictures I promise! I am really excited to meet her and be around her."

Renae got her wish during their practice sessions but the same didn't go for the American Idol audiences. In the footage of the rehearsals, The Chandelier hit-maker's face was blurred out.

The Elastic Heart singer has taken great efforts to keep her identity hidden in order to have some semblance of privacy. And while her face has been most often covered by those long fringed wigs, she has "let her hair down" on occasion and allowed the cameras to get a glimpse of her face.

Most recently, at the annual Spotify Creators Party in Los Angeles in February, the Grammy-nominated songstress walked the red carpet sporting an oversized bow wig but later took it off while mingling with fellow-celebrities.

The next episode of American Idol 2016 will air on Thursday, 31 March on 8 p.m. EDT on Fox.