In 2019, Franco's body was moved from a mausoleum at the Valley of the Fallen mass grave memorial to a private family burial plot, a decision the country's socialist Prime Minister Pedro Sanchez described as "an end to the moral insult that the public glorification of a dictator constitutes."

The death of Almudever, who the couple met during their research, is not the end of the whole story, just the International Brigade chapter, as his brother Vicente, who was in the Republican army, is still alive, aged 104.

Groups such as the International Brigades Memorial Trust in the United Kingdom promote education about the war and the many memorials to volunteers that can be found across Britain and Ireland, including the national memorial to the 526 British and Irish dead, situated on the South Bank in central London.

"We want more people to know it was a truly global war, the whole world was going to Spain," said Hwei-Ru.

"Those people's spirit was so selfless. They didn't ask if they could win or not, or if they were going to die or not; they just thought they must go. What they did, they did for the good of humanity."