Christina Aguilera hit something of a bum note with her much-hyped Whitney Houston tribute at today's American Music Awards - and one former musical rival stole the show with an instantly viral reaction shot.

Aguilera took to the stage to perform a medley of songs from Houston's film The Bodyguard, which turns 25 this year. She opened with arguably the late diva's signature song, I Will Always Love You - and despite her powerhouse vocals, proved that Houston's iconic performance is hard for anybody to live up to.

Cameras cut to fellow pop star Pink in the audience, her eyes locked on Christina, her expression - what? Pain? Concentration? Sadness? Horror? Who knows:

The cameras cut to Pink again later in the song, and her expression had by then softened - she was shown smiling and applauding. After the performance, she was quick to clear up any confusion about her feelings towards her old Lady Marmalade singing partner.

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"Christina f***ing killed it tonight for one of our favourite singers ever. This about Whitney, and I am in awe of Christina's talent. Show the clip where I'm in tears, you negative Nancy's," she tweeted.

Aguilera followed up that classic song with snatches of other Bodyguard hits I Have Nothing and I'm Every Woman - but viewers at home were still stuck on that reaction shot from Pink.

Others were entirely distracted during Aguilera's performance by the Genie In A Bottle singer's sudden apparent resemblance to Australian-born rapper Iggy Azalea: