UK government plans to present former Chilean President Patricio Aylwin with a family tree showing his Welsh roots were derailed after a genealogist discovered his family wasn’t actually Welsh, newly declassified files have revealed.

The Foreign and Commonwealth Office (FCO) commissioned research into Aylwin’s heritage prior to a state visit in April 1991 and discovered the former Chilean premier’s great grandfather, Richard Aylwin (who later changed his name to Ricardo Aylwin), emigrated to Chile in 1833.

President Aylwin always believed his family to be Welsh and had planned a trip to Cardiff as part of the official UK visit which followed his election as Chile’s first democratically elected premier after the 16-year dictatorship of Augusto Pinochet.

The FCO asked Timothy Duke of the College of Arms, the official heraldic authority for England, to research Aylwin’s family tree, Who Do You Think You Are? Magazine reports.

However, having checked wills, parish registers, marriage licences and other sources, Duke concluded that the Aylwins were English – not Welsh.

“They turned out to be tallow chandlers in London and then they were yeoman farmers in Sussex, where Aylwin is quite a common name,” he recalled.

Richard Aylwin’s father, Robert Patrick Aylwin, was baptised in Haslemere in Surrey in 1762. The family’s only Welsh link came from Robert Patrick’s brother, George Allen Aylwin, an oil broker, and his son Frederick Arthur Aylwin, who had business interests in the principality.

Following the revelations, Duke accompanied Aylwin on a visit to the villages of Treyford and Didling in Sussex, where the president visited the graves of his ancestors and met relatives.

“He didn’t speak English so we had an interpreter, but he was delighted with the reception he got in Sussex,” Duke said. “He just seemed delighted to be back in a county from which his forebears had come and to discover the truth.”