BTS star Jin began his 18-month mandatory military service on Tuesday.
Before enlisting, the 30-year-old, who is the oldest member of the K-pop group, posted a photo of himself sporting a new military buzzcut on Korea's Weverse social media app, which he captioned, "Cuter than I expected."
In a separate post, he wrote, "It's time for a curtain call."
Jin entered the Yeoncheon army base in the northern Gyeonggi province - just 10 miles (16 kilometres) from the Demilitarised Zone that separates South Korea from North Korea - at 2 pm local time on Tuesday.
A motorcade of six black vans, assumed to carry Jin and his security staff, drove past fans and media to enter the base. Devotees of the group had gathered outside despite a warning from the pop star to stay away from the base during his training.
According to the country's Defense Ministry, the singer has begun five weeks of basic military training in the bootcamp near the North Korean border. He will then be assigned to an army unit.
South Korea is still technically at war with North Korea, despite a 1953 armistice that formally ended open hostilities after a three-year war. All able-bodied men are required to serve in the country's army for 18 to 21 months.
In October, BTS' record label and management firm Big Hit Music confirmed that all seven members of the group were planning to undertake military service. They are expected to reconvene as a group around 2025.
Jin had submitted a request to delay his conscription but later withdrew the plea. Busan's mayor had also contested the group's conscription, asking South Korea's President Yoon Suk-yeol to exclude the pop stars from national service. The president declined the request.
