South Korean spies have finally come up with a definite answer to the mysterious public absence of North Korean leader Kim Jong-un, which they say was caused not by cheese but by a cyst.

Kim disappeared from the public eye for six weeks between September and October, sparking wild speculation about his health as well as the state of public affairs in the Hermit Kingdom.

Some reports claimed the Supreme Leader was suffering from gout or had broken both ankles due to his obesity and needed to shed weight due to a gluttonous addiction to Swiss cheese.

Others suggested the possibility that a coup was taking place and his younger sister Kim Yo-jong was now in charge.

However, according to South Korea's intelligence agency, Kim was recovering from surgery to remove a cyst from his right ankle.

The National Intelligence Agency (NIS) told lawmakers in Seoul that a foreign doctor was invited to the reclusive country to perform the operation, two MPs told news agency Yonhap.

Lee Cheol-woo of the ruling Saenuri Party and Shin Kyong-min of the opposition New Politics Alliance for Democracy said the spy agency briefed them on the matter in a closed-door meeting.

They said the NIS added it was possible that Kim's condition could recur, as his ankles were exposed to extra strain due to his many official inspection tours and obesity.

The young leader, believed to be 31, was last seen walking with a limp on 3 September during a concert in Pyongyang. He reappeared in state media hobbling with a cane in mid-October.