JUSTIN BIEBER FORGETS LYRICS WHILE PERFORMING WITH ARIANA GRANDE

The 21-year-old singer rocked up at the American Airlines Arena unexpectedly to perform her hit 'Love Me Harder' with the brunette star but was left red-faced when he forgot the words.

After the song, Justin apologised for his blunder, telling the audience, "I feel a little bad, I forgot the words. Ariana, I've been trying to memorise it backstage for like an hour."

He added while giving Ariana, 21, a hug, "Can you guys forgive me for forgetting the words? I feel terrible."

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But it seems Justin couldn't stop thinking about his mistake as he took to his Instagram account later on to share a photograph of himself on stage with his arms wrapped around the Bang Bang singer and wrote, "Had fun with u Ariana, even tho I forgot all the words haha (sic)."

Justin's embarrassing mishap didn't seem to bother the 21-year-old starlet as she took to her Twitter account after the show to thank him for his performance.

She tweeted, "thank u miami babes and thank u @justinbieber (sic)." She also shared a video clip of her and Justin singing his song As Long As You Love Me, which usually features a rap from her boyfriend Big Sean.