Is Kim Jong Un's little sister Kim Yo Jong running North Korea?

That's what the Global Post's Geoffrey Cain wants to know as rumors swirl around the question of the Supreme Leader's health.

Kim has not made a public appearance since Sept. 3, when he attended a concert with his wife. Before that, he was seen walking with a limp.

Late last month, the state-run Korean Central News Agency said the enigmatic 31-year-old dictator had been suffering from "discomfort," but would not elaborate.

That has led to speculation that Kim's younger sister, Kim Yo Jong, may be managing North Korea's affairs in her brother's stead.

"She is one of the only people [in North Korea] that we know has unfettered direct access to KJU," Michael Madden, editor of the North Korea Leadership Watch blog, told the Global Post.

Kim Yo Jong, who was born in 1987, is the youngest of Kim Jong Un's seven known brothers and sisters. She attended boarding school in Switzerland with him, according to Madden, but has otherwise kept a low profile.

Kim Yo Jong (IBT)

In March, she made her first official appearance on state television, casting her vote in North Korea’s parliamentary elections.

"At the present time, I would not be surprised if she is sole gatekeeper," Madden said.

It's not the first time Kim Jong Un's absence has drawn the attention of Pyongyang-watchers. In June 2012, Cain notes, he went missing for 24 days, and at least two other unexplained instances have been noted where he disappeared from the public eye for more than two weeks.

It's also not the first time a mysterious young woman has sparked the curiosity of North Koreans.

In July 2012, a mystery woman appeared with Kim on North Korean state television during a ceremony marking the 18th anniversary of the death of North Korea's founder, Kim Il Sung (Kim Jong Un's grandfather). The same woman was seen in a photograph showing Kim and others clapping during a performance by a band in Pyongyang, leading to furious speculation about her identity.

The mystery woman, it turned out, was Kim Jong Un's wife, Ri Sol Ju, state-run media announced later that month.