William Cassandra Rosamonte Barbosa (born 18 December 1983) is a São Toméan footballer who plays as a centre back for Portuguese club AD Quinta do Conde.
He was capped by the São Tomé and Príncipe national team.
Barbosa left his natal São Tomé for Ceará, Brazil in 2009 to study nursing at Fortaleza-based Uniclinic.
However, a short time later he joined the university football team and, due to his performances, he dropped the studies out to pursue a career as a footballer.
This biographical article related to Santomean association football is a stub.