In response to global climate change, numerous taxa are expanding their living ranges. In species with highly migratory aptitudes such as sea turtles, this expansion may be driven by individuals either from nearby or distant areas. Recent observations suggest a range expansion of the philopatric green turtle (Chelonia mydas) to the central and western Mediterranean. To assess the origin of the turtles found in these novel habitats, we first built a genomic baseline, using 2bRAD sequencing on individuals from regular nesting areas in three Regional Management Units (RMU): North Atlantic, South Atlantic and Mediterranean (5 individuals from each RMU). Secondly, we compared this baseline with genotyped hatchlings from three nests laid in new Mediterranean sites and four mature-size green turtles tagged with satellite telemetry in the western Mediterranean basin. Our analyses revealed that the nest in Tunisia was sired by turtles from the South Atlantic RMU, while the two nests in Crete were sired by turtles from the Mediterranean RMU. In addition, the three adult turtles sampled in southwestern Mediterranean were genetically assigned to the South Atlantic RMU while the remaining individual within reproductive size, sampled in northwestern Mediterranean, was genetically assigned to the Mediterranean RMU. These results suggest a simultaneous potential colonisation by two distant regions. We propose that the range expansion of green turtles into the central and western Mediterranean, as also already observed in loggerhead turtles (Caretta caretta), is likely driven by climate change and these populations may become globally important as temperatures continue to increase.