The book, ‘The Secret Son of Franco’, claims the child was the product of an affair with the wife of a lieutenant under his command.

Spanish author Fernando Gracia will launch his new book in the Tenerife capital of Santa Cruz next week (April 20).

The book will allege that the child was born just before Franco launched a failed attempt to overthrow Spain’s Socialist government in 1936, an action he directed from his base in La Esperanza, Tenerife, and which set in motion the bloody Spanish Civil War.

He became leader of the right-wing Nationalist movement during the Civil War and became head of state when the Republican forces were defeated in 1939. He ruled until 1975, presiding over what was for many years a harsh and brutally repressive regime.

Franco was a staunch supporter of the Roman Catholic church while in power, which is why the new book will be seen in Spain in such a controversial light.