Bristol died Sunday at St. Joseph Mercy Livingston Hospital in Howell after suffering an apparent seizure at his Brighton Township home, the Ann Arbor News reported.
Bristol's girlfriend called 911 at about 5 a.m. Sunday to say Bristol was ill and needed an ambulance, police said.
Police said they were "99.9 percent positive" Bristol died of natural causes.
The North Carolina native worked as a singer, songwriter and producer during his 40-year career in Motown.
He is best-known for his song "Someday We'll Be Together," which was a No.1 hit by the Supremes in 1969. Bristol sang background vocals on the record.
Bristol stayed with Motown for the duration of the 1960s, writing and producing for Stevie Wonder, Diana Ross, Marvin Gaye and Tammi Terrell, Smokey Robinson, Michael Jackson, Martha Reeves, Jimmy Ruffin, the Four Tops, The Detroit Spinners, the late Edwin Starr, David Ruffin and Junior Walker.
After leaving Motown, Bristol worked as a solo artist and had a hit in 1974 with the song, "Hang On In There Baby."
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