Shin Okamoto, the former vocalist of the band The Jaguars, was found dead in his Tokyo apartment bathroom on Sunday. He was 59.

Monday would've been Okamoto's 60th birthday, and his friends had planned to celebrate early with a party on Sunday. However, his former bandmate Hisayuki Okitsu (62) had been unable to contact him since Saturday, so the worried Okitsu asked a friend to check in on Okamoto. She arrived at his apartment in the afternoon, only to discover Okamoto's naked body in the bathtub.

Police found no signs of injury or indication of suicide, so it appears to have been a natural death. The specific time and cause of death are currently being determined.

The Jaguars were part of the Group Sounds movement during the 1960s. The band shot to fame in 1967 after their debut single, "Kimi ni Aitai," became a million seller. The group disbanded in 1971, though Okamoto continued his career as a solo musician and musical actor. Divorced once, Okamoto lived alone. He had been fighting illness for the past few years.