The 30-year-old posted a photo of himself with his new military haircut before enlisting on Tuesday. “It looks cuter than I expected,” he said.
As South Korea is still technically at war with its hostile neighbour North Korea, all able-bodied men are required to serve in the army.
Jin has begun five weeks’ training at a bootcamp near the North Korean border.
After this, he will reportedly be assigned to a frontline unit. This news sent his millions of adoring fans into a frenzy.
So, what can Jin expect from his time on the frontline?
At the Yeoncheon bootcamp, where Jin has enrolled, recruits sleep on mats on the floor, in rooms with 30 people. They are taught how to handle weapons and fire live ammunition before being put through demanding wartime scenarios.
Cadets told us that the most challenging tasks they faced were being sealed in a gas chamber, to experience the effects of CS gas, and having to detonate a live grenade.
“I was pretty nervous to hold the grenade and shocked to learn how powerful it was,” said 22-year-old Yang Su-yeon, who completed his training at Yeoncheon last year.
“It was physically demanding, but mentally it was okay. The drill sergeants were all friendly,” Yang said.
After training, Jin will reportedly be stationed near the North Korean border, with a frontline unit.
North and South Korea are separated by a 4km (2.5-mile) wide strip of land, which runs along the length of their border, known as the Demilitarized Zone (DMZ). Both sides are fenced off with barbed wire and heavily armed.
Yang spent his service as an out-post guard at the DMZ, with the 5th Infantry Division, which is one of the most frontline positions. He would keep watch through the night, constantly surveying the North Korean soldiers on the other side, using thermal imaging equipment.
“Please take care and bring enough warm clothes and medicine,” wrote Maliah Leah. “I hope your colleagues treat you well. We will be waiting patiently for your comeback.”