The Sun reports how Melissa, who not only looks like Jessie but is also the same age and shares a similar upbringing and heart defect, was spotted in the audience.
"Oh my God, you're freaking me out," Jessie reacted on seeing what could've quiet possibly been a long lost twin sister.
Model Melissa currently works as a Jessie J look-a-like, having even confused agencies when scouting for work.
Melissa, told the newspaper: "The resemblance is more than uncanny — we look like identical twins. I sent a picture of myself to a lookalike agency and the boss called to say, 'We need a picture of you, not Jessie J.'
"People ask me for my autograph in the street."
And the 23-year-old from Milton Keynes has also been mistaken for the real thing by the 'Domino' star's own security team.
Recalling how she was once stopped by a guard at a Jessie J gig, Melissa revealed: "He told me, 'What are you doing here? We need to get you to the performers' entrance.'
"But there is one big difference between us — I can't sing a note."
Check out pictures for the pair together on The Sun website and tell us what you think!