Justin Bieber makes impromptu duet with Ariana Grande

Justin Bieber surprised Ariana Grande on stage at her Honeymoon tour in Miami on Saturday.

The 21-year-old singer rocked up at the American Airlines Arena unexpectedly to perform her hit ‘Love Me Harder’ with the brunette beauty 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.”

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’ hitmaker and wrote: “Had fun with u Ariana, even tho I forgot all the words haha (sic).”

The ‘Boyfriend’ hitmaker’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.

Alongside the footage of her rapping her beau’s part, she said: “rapping my baby’s verse @bigsean with @justinbieber last night at my show (sic).”