The Balkan Peninsula is one of the greatest hotspots for biodiversity in Europe. While the region has been investigated thoroughly, some parts remain understudied and may still harbour undiscovered diversity, even in well-studied organisms such as Lepidoptera. Here we investigated the group of the so-called anomalous blue butterflies, also known as ‘brown complex’ of the subgenus Agrodiaetus Hübner, 1822 including the taxa of the entire Polyommatus aroaniensis (Brown, 1976) species complex. This species complex is distributed in the southern part of the Balkan Peninsula and known to be represented by three closely related allopatric species, differentiated by their chromosome numbers (n) and mitochondrial (mt) DNA. These are P. aroaniensis sensu stricto (Southern Greece, Peloponnese, n=47–48; mt haplogroup aroa1), P. timfristos Lukhtanov, Vishnevskaya et Shapoval, 2016 (Central Greece, Attika, n=38, aroa2) and P. orphicus Kolev, 2005 (North-Eastern Greece, Southern Bulgaria, n=41–42, orph1). Based on an analysis of chromosomal, molecular and morphological markers, we demonstrate that a fourth taxon of this species complex exists in Albania. This taxon possesses the mt haplogroup aroa3, which is the most differentiated within the entire P. aroaniensis species complex, and the karyotype (n=42–43), which differs by one fixed chromosome fission from P. orphicus. The Albanian taxon seems to be ecologically specialised (habitat on dark-coloured, ophiolitic substrate soils) and differs in colouration (wing reflectance) from the others taxa of the P. aroaniensis species group. Based on the evidence here presented and following the current view of the taxonomy of the group, we propose considering the Albanian taxon as a new species, here described as Polyommatus luraesp. nov. At the contact zone between the new species and P. orphicus, in addition to typical ones, we detected specimens with haplogroup orph2, karyotype n=43 and intermediate morphology, which seem to represent P. lurae × P. orphicus hybrids.