Thomas Neuwirth, who won the 2014 Eurovision Song Contest performing in drag as Conchita Wurst, has announced that he is H.I.V. positive, saying a threat of blackmail prompted him to make the news public.

In a statement posted on the official Conchita Wurst Instagram account on Sunday, Mr. Neuwirth said he has been H.I.V. positive for “many years” and had not intended to discuss the diagnosis publicly.

“An ex-boyfriend is threatening me to go public with this private information,” Mr. Neuwirth wrote on Instagram, “and I will not give anyone the right to frighten me and affect my life in the future.”

A spokesman for the performer said in an email that Mr. Neuwirth was not available for further comment. He also clarified that Mr. Neuwirth’s preferred pronouns are “she” for references to the stage persona of Conchita Wurst and “he” for Mr. Neuwirth, the private individual.