Christina Aguilera joined A Great Big World for an unforgettable performance of their hit ballad Say Something at the American Music Awards 2013.

Singer Jennifer Hudson introduced the performance before the duo started on stage.

Aguilera later joined them with an entrance of flawless harmony. She kept her stage presence elegant and didn't stray too far away from her mic stand. She donned a classy and floor length, black dress with a scooped neck and no sleeves. She completed her simple look with a braid headband hairstyle with a low, centered bun. Her makeup was very natural looking with soft, gold eyes and a light pink gloss.

She was an obvious favorite of the night as Christina Aguilera was trending worldwide on Twitter along with her first hit song Genie in a Bottle.

The performance was a simple one with dim lighting and a piano for A Great Big World members Chad Vaccarino and Ian Axel.

Many of Aguilera's fans noted on Twitter her performance was "heartwarming" and "touching." Some also recognized her weight loss compared to last year's show. While she performed with A Great Big World, she certainly held her own and added to the flawless harmonies.

The duo recently opened up about what it was like to record the song with the What a Girl Wants singer.

Vaccarino said, "We could not be happier with how [Aguilera] did, how the recording came out. It's amazing."

He added that Aguilera opted out of her recognizable belting and high notes and decided to "let the song just be.It makes you kind of feel the longing [of the song]."

Axel chimed in and said Aguilera wanted to be open with the song.

"We've never heard her sound so vulnerable. From what she's told us, she's in a different place in her life, and she only wants to take on projects that inspire her, so we're super honored."