Curtis was the lead singer with the band in 1967 when it released its number one hit Baby, Now That I’ve Found You. It has been claimed that the song was the first by a multi-racial band to top the charts.
Curtis was born in Trinidad and moved to the UK as a teenager to pursue a career as a boxer. Afterwards, he started singing with the band, before going on to lead a solo career in the 1970s. Curtis also appeared in musicals in London’s West End.
Curtis’s wife told the BBC earlier this year: “Unfortunately he has been diagnosed with two cancers. Doctors cannot do anything about it.
He had left the band before it released perhaps its best known song Build Me Up Buttercup.