All able-bodied men in South Korea must serve at least 18 months in the military.

After a years-long debate about whether BTS deserved an exemption, Jin, the oldest member of the group, enlisted last year and his bandmates J-Hope and SUGA followed this year.

RM and V were set to begin their five-week basic training at an army boot camp in South Chungcheong province on Monday, the Yonhap news agency reported.

RM -- whose full name is Kim Nam-joon and is the leader of BTS -- posted a message to fans late Sunday, saying it will be "a time of learning and new inspirations".

"Goodbye for now. Let us be us, whenever and wherever! Let's meet in the future," he wrote on social media platform Weverse.

V -- real name Kim Tae-hyung -- shared selfies donning his newly shorn, military-approved buzzcut with sunglasses and a scarf.

"It has been a dream to wear sunglasses with a shaved head. I wanted to try it someday and it worked out well," he wrote Sunday on his Instagram account.

The septet has become a global cultural phenomenon, selling out stadiums around the world and dominating key US charts while raking in billions for South Korea's economy and building an international legion of fans known as ARMY.

Their label BIGHIT MUSIC had confirmed in November that the last four members of the group would enlist, but did not disclose additional details.

The two remaining members, Jimin and Jung Kook, are due to enlist on Tuesday, according to local media.