For more than a century, speculation about the Japanese emperor's Korean roots was mostly restricted to lofty academic journals and idle coffee shop gossip.
But this week, the historical debate was surprisingly joined by a new scholar who has as much claim as anyone to be an authority on the subject: the emperor, Akihito, himself.
To the delight of South Korea and, no doubt, the silent fury of many Japanese nationalists, the current holder of the Chrysanthemum Throne used a 68th birthday press conference last weekend to celebrate his mixed origins.
Looking ahead at a year when the two countries will co-host the World Cup finals, Akihito said he felt personal attachment to Korea because of the blood ties of his ancestors.
"I, on my part, feel a certain kinship with Korea, given the fact that it is recorded in the Chronicles of Japan that the mother of Emperor Kammu was of the line of King Muryong of Paekche," he told reporters.
Kammu, reigned Japan from 781 to 806 AD, while Muryong ruled the Paekche Kingdom in Korea from 501 to 523 AD.
Although he was quoting historical records, it is the first time that an emperor has publicly lauded the Korean blood in the imperial line.
According to Japanese myths, the Chrysanthemum Throne can be traced back more than 2,600 years to the sun goddess Amaterasu Omikami in the dawn of creation.
Those myths were officially discarded at the end of the second world war when emperor Hirohito was forced to renounce his divine status by the American occupation forces.
But the imperial household agency still claims Japan has the oldest imperial line in the world, unbroken across 125 generations. Although no longer a god, the emperor is still seen by Shinto priests as having an "airlike existence".
The constitution merely declares him to be the symbol of the nation. Academic debates about his ethnic and national "purity" have made little progress. The imperial household agency have reportedly made archaeological sites in the former capital of Nara off-limits because officials fears the discovery of evidence that emperor's Korean ties are far stronger than has long been taught in Japanese schools.
Last weekend, however, Akihito did nothing to dispel such associations by acknowledging that much Confucian and Buddhist teaching, as well as court music, came via the peninsular. "I believe it was fortunate to see such culture and skills transmitted from Korea to Japan," he said.
The emperor's comments induced dramatically different reactions from the two nations. In Japan, the story proved hard to stomach. It was covered in detail only by the Asahi Shimbum. Other major newspapers either mentioned the Korean ancestry issue only in passing or ignored the statement altogether.
In South Korea, however, it was front-page news and generated much editorial praise. Government spokesmen welcomed the comment as a sign of a possible thaw after a year in which bilateral relations were marred by fierce disputes over Japanese prime minister Junichiro Koizumi's visit to the controversial Yasukuni war shrine and the approval of a new history textbook that South Korean believe is a whitewash of Japan's wartime atrocities.
South Korean politicians expressed hope that it would pave the way for Akihito to attend the world cup opening ceremony in Seoul on May 31.
But no Japanese emperor has visited South Korea since the war and the imperial household agency says there are no plans for this situation to change.
Nationalist politicians are said to be opposed to an imperial visit, fearing that Akihito would come under pressure to make a new apology for Japan's wartime misdeeds.
Reading between the lines of the emperor's comments last week, however, it would seem that he is more than willing to travel to Seoul next May, making the opposite journey to that made by his Korean ancestors.
