Youngseo

Biography

Lee Young-seo (Korean: 이영서; born November 13, 2005), known mononymously as Youngseo, is a South Korean singer. She is a member of the South Korean co-ed group AllDay Project under The Black Label. Youngseo first gained public recognition as a contestant on the 2023 survival show R U Next?, where she placed second and was selected for the original lineup of the girl group Illit. Following her departure from Belift Lab in early 2024 before the debut of Illit, she has established a significant individual presence through high-profile fashion editorials and solo brand collaborations.

2023–2024: R U Next? and departure from Illit prior to its debut

In June 2023, Youngseo was introduced as a contestant on R U Next?, a reality competition series aimed at forming a new girl group called Illit under Belift Lab. Throughout the program, she was consistently noted as one of the most popular trainees, eventually placing second overall in the finale on September 1, 2023. On January 5, 2024, Belift Lab announced that Youngseo had mutually agreed to terminate her contract and would no longer debut with Illit. Her departure generated significant media discussion, with publications describing her as a "standout trainee" whose future steps were highly anticipated by fans. In late 2025, reports emerged regarding allegations of mistreatment during her time as a trainee, with claims that Youngseo and other trainees were pressured to drop out of school to focus on their training.

2025–present: Debut with AllDay Project and solo activities

On June 9, 2025, The Black Label revealed Youngseo as a member of their new co-ed group, AllDay Project. The group officially debuted on June 23, 2025, with the single album Famous. In an interview following her debut, Youngseo discussed her industry struggles, revealing that she faced significant self-doubt and initially believed her career window had closed before joining The Black Label, admitting she had previously felt "too old" to be an idol.
Youngseo has contributed to AllDay Project's music as a lyricist, with credits on tracks such as "You and I". In an interview with Clash Magazine, she discussed her active involvement in the track, noting that she spent significant time studying how to execute and express its vocal-heavy arrangements to showcase a new side of the group.
In November 2025, Youngseo participated in AllDay Project's performance at the inaugural Korea Grand Music Awards (KGMA). Following the event, where the group made history by winning the Grand Prize (Daesang) as a rookie co-ed ensemble, media attention surrounding Youngseo intensified and led to making her first independent projects in early 2026, including her debut solo magazine cover for the January issue of W Korea, which included a digital cover campaign in collaboration with the brand UGG. In March 2026, she appeared in solo pictorials and interviews for Elle Korea, where she was described as having a "definite cat-like charm", and shared insights into her personal life and style preferences, stating that she "loves everything cute that exists in the world".

Public image

Youngseo is frequently cited by South Korean media as a "standout member" of AllDay Project due to her extensive pre-debut history and established fan base from R U Next?. Her "cat-like" visuals and fashion-forward image have made her a sought-after model for digital campaigns and editorial features, often being highlighted alongside fellow member Annie Moon for their significant public impact prior to the group's official launch.

Endorsements

In early 2026, Youngseo collaborated with the American fashion brand UGG for a digital cover campaign. She has also participated in a rendezvous feature for Issey Miyake's perfumes in W Korea.

Songwriting credits

All song credits are adapted from the Korea Music Copyright Association, unless cited otherwise.