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Billboard has included Korean girl group TWICE in its Annual 21 Under 21 list "of powerful young voices includes arena headliners and promising new talent, familiar names and new musicians quickly rising toward the mainstream."

The ranking is composed of 21 "brand-new stars crashing into the Top 5 to list mainstays still representing the power of youth to the No. 1 artist taking the top spot for the first time," Billboard said.

TWICE, composed of members aged 18-22, is listed at No. 18.

"Formed by JYP Entertainment in 2015, this robust collective delivers a combination of catchy hooks, kooky concepts and ­choreography that nabs it consistent No. 1s in Korea, while its 2017 EP 'Signal' landed at No. 3 on the World Albums chart," according to Billboard.

TWICE is thankful for being included on the list, saying, "The great love we have been receiving is still ­dreamlike" but said that they are still new and "we still need to grow."

Shawn Mendes, 19, topped the ranking.

According to Billboard, "Since learning to play guitar at the age of 13 in 2012, Mendes has redefined the mainstream appeal of modern teenage songwriting."

Mendes' 2015 album "Handwritten" and last years' "Illuminate" ranked first on Billboard 200 while the song "There Nothing Holdin' Me Back" is in the top 20 on Billboard Hot 100.

His summer concert tour has grossed more than $32 million, Billboard added.

"I can't believe how fast things have happened and I'm just so honored that people are able to look to me as a leader," he said.

Mendes is followed by Lorde, 20 years old; Khalid, 19; Lil Yachty, 20; Camila Cabello, 20; Kodak Black, 20; Grace VanderWaal, 13; Hailee Steinfeld, 20; Grace VanderWaal, 13; CNCO, 16-21; Desiigner, 20; Noah Cyrus, 17; Daya, 18; Alan Walker, 20; Becky G, 20; Jake Paul, 20; Why Don't We, 16-19; Zara Larsson, 19; TWICE, 18-22; PRETTYMUCH, 17-20; Chloe x Halle, 17, 19; and Sabrina Carpenter, 18.