A number of theories seek to explain why one of Korea's most popular couples called it quits earlier this week, but one idea holds supreme.

With the sad news that Girls' Generation member Yoona (Im Yoona) and singer-actor Lee Seung Gi had called it quits after dating for a year and nine months, many fans took to the internet to try and explain why the popular couple ended their relationship.

Sources close to the pair cited the stars' busy schedules as motivation for the split. In true die-hard fan fashion, that explanation left a lot of questions unanswered, prompting fans to dig a bit further into the situation.

One prominent theory centers on South Korea's mandatory military service, which Lee Seung Gi still has not completed. The actor's impending military enlistment was cited by many as one of the main reasons for the breakup, according to forum comments translated by Netizen Buzz.

"I am glad [they broke up] since Lee Seung Gi has to go to army soon," said one commenter. "Seung Gi, let’s go to army now. There is nothing holding you back now right?" asked another. "They're probably too busy, but they most likely broke up because it's time for him to go to the army," read another comment.

During a recent press conference for Girls' Generation's OnStyle reality show Channel Girls' Generation, Yoona revealed that she will prioritize the group's promotions over her "personal matters."

Lee Seung Gi has not announced any specific plans to enlist.