SEOUL, South Korea -- Five hundred years of Korean royal blood flowed in Yi Ku, but he lived in such obscurity in Japan that when he died of a heart attack in a hotel room last week his body was not discovered for two days.

Nonetheless, thousands of mourners in black suits and traditional white robes followed the coffin of the last direct heir to Korea's throne through the streets of Seoul on Sunday, paying their final respects to the dynasty that ruled the peninsula from 1392 until 1910.

Yi, the son of Korea's last crown prince, died alone of a heart attack at age 73 in his hotel room July 16 in Japan, where he lived for most of his life. His body was discovered Monday.

Japan forced Yi's grandfather from power in 1907 and annexed Korea in 1910, ending the centuries-long reign of the Chosun Dynasty. After Korea's liberation at the end of World War II in 1945, the royal family was not immediately allowed to return for fear it would meddle with the new government, extending Yi's years of exile.

"May he join his parents in enjoying all the happiness that he did not enjoy in this life," Korea's Prime Minister Lee Hae-chan, a relative of Yi, said in a funeral address at Changdeok Palace.

Yi was born in Tokyo in 1931 to Yi Un, the Chosun Dynasty's last crown prince, and Princess Yi Bang-ja, a Japanese royal family member. Four members of the Japanese royal family attended Sunday's funeral, South Korea's Yonhap news agency reported.

He was raised in Japan and finished his education at the Massachusetts Institute of Technology, majoring in architecture and living largely apart from the Korean public. He was more fluent in Japanese and English than Korean, a sore point with his family.

Yi married a German-American, Julia Mullock, in New York in 1958. The couple returned to Korea in 1963 and lived in the Changdeok Palace until he moved to Japan for good in 1977 after a business failure. The couple divorced in 1982. They did not have children.

Mullock watched Sunday's ceremony from across the street from the palace, South Korea's YTN news channel reported.

Mourners in the crowd acknowledged the passing of an epoch in Korean history with Yi's burial.

"Like most other people, I came to pay respects to the last imperial grandson. It's his last passage," said Lee Seung-hae, 28, a graduate student in Seoul.

Yi Ku was buried in the royal burial grounds east of Seoul, alongside his parents and his brother, who died as an infant.