A group that celebrates the republican pilots who fought fascism in the skies over Spain has condemned the vandalism of a memorial stone to a German airman that was looked after by an unlikely visitor – the Spanish ace who killed him. Friedrich Windemuth, a member of the notorious Condor Legion sent by Hitler to aid Franco during the Spanish civil war, died after being shot down over northern Catalonia by the Spanish pilot José Falcó in February 1939. The German fighter pilot’s body was repatriated but a memorial stone was put up close to where he died. Falcó, who fled into exile after Franco’s victory and died in 2014, would often visit the stone and lay flowers for his fallen adversary. “We ended up facing off against each other and he died, but it could have been me,” Falcó told La Vanguardia in 2009. It emerged this week that Windemuth’s stone – which sits near vineyards and a cypress tree by the side of the road between Vilajuïga and Garriguella in Girona province – had been smashed in half. It had read: “Here, on 6.2.1939, in the fight for a nationalist Spain, fell Friedrich Windemuth, born 27.5.1915 in Leipzig.” The Association of Republican Aviators (Adar) said it was deeply saddened by the act of vandalism. “The stone was often visited by Falcó, who used to tidy it and lay flowers in memory of the enemy who fell in a fight that, as he himself noted, could have ended in his own death,” Adar said in a statement. “The stone was also attacked in 2009 by someone who must have been ignorant of the posthumous honour that Falcó displayed towards his opponent.” Falcó, who had lived in Algeria and then France, eventually returned to Spain to visit. “I found the stone thanks to a local farmer, because I didn’t even know it existed,” he told La Vanguardia. “I saw how old the pilot had been and realised we were almost the same age. Perhaps even his family didn’t know the stone was still standing.” Antoni Valldeperes, the president of the regional delegation of Adar, said Falcó had been upset by the 2009 attack on the memorial stone. Valldeperes also told El País that while whoever was responsible may have thought they were destroying something that praised fascism, they had in fact attacked “historical memory and the dignity of the combatants”. He added: “In a way, it was also a monument to Falcó and the way in which he honoured the memory of his enemy.” The deployment of the Condor Legion, infamous for bombing the Basque town of Guernica in 1937, allowed the Nazis to practise their blitzkrieg tactics, which were later used in the second world war. Windemuth’s stone is not the only lingering trace of the legion’s presence. Five years ago, at the request of the German embassy, Madrid’s city council dismantled a mausoleum in La Almudena cemetery where seven Condor Legion pilots are buried. The monument was inscribed in German: “Here rest the German pilots who fell in the struggle for a free Spain.” Underneath, in Spanish, it read: “German aviators who died for God and for Spain. Present!” The German embassy in Madrid had asked for the facade to be removed before the 80th anniversary of the Guernica massacre in 2017. In a letter, the German ambassador requested that “the dismantling should include the removal of the entire facade” and that it be replaced with “seven small and simple plaques to identify those buried there”.