Strictly Come Dancing voiced their frustration over the opening number on Sunday's results show after they made the same realisation.
The dance contest on November 21 opened with a Wicked theme routine to the song Defying Gravity during Musicals Week.
Pro dancers were cast as the lead roles Elphaba and Glinda from the musical classic with vocals from the Strictly Come Dancing house band singer.
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But fans watching at home pointed out that West End and Broadway musicals legend Cynthia Erivo, who was sitting right there on the judging panel, would have been a better option.
Cynthia, who was a guest judge on the show this weekend, has just been cast as Elphaba in the film adaptation of Wicked with singing superstar Ariana Grande.
She was a big hit with fans during the live show on Saturday night after launching into sign language to comment on Rose Ayling-Ellis and Giovanni Pernice's Frozen routine.
After communicating with sign language for Rose, who is the BBC dance show's first deaf contestant, she said: "You're joyful, beautiful.
@kookieseokjins fumed on Twitter: "Ok I'm behind but why did they not get Cynthia to sing for Elphaba she's right there."
@alexx_shaw tweeted: "Fancy having Cynthia Erivo, the newest Elphaba for Wicked!, on the show but not getting her to sing Defying Gravity...?!
Another outraged viewer @EmmaHSinger commented: "YES A WICKED DANCE! However the fact that they literally have Cynthia Erivo -literally about to play Elphaba in the Wicked movie-and they didn't let her sing Defying Gravity is actually a crime."
@mrsspanner said: "I mean you’ve got a professional Elphaba judging this week, could Cynthia not have sung Defying Gravity? #Strictly"
And @JessicaMTemple gasped: "OMG those chords played and I thought we were gonna get a listen at Cynthia’s Elphaba already."
After years of speculation, the official news recently broke that Cynthia and Ariana were starring in Universal’s film.
Wicked opened on Broadway in 2003 and remains its fifth longest-running show.
The original Elphaba and Glinda were Idina Menzel and Kristin Chenoweth.
