Real-time PCRs were developed to characterize Fomes fomentarius lineages occurring in the beech forests of the Ardennes (southern Belgium). A collection of F. fomentarius sensu lato isolates was built up in 2020 and 2021 from basidiocarps developing on beech trunks, stumps, or logs. Two of the 148 isolates tested (monokaryotic and dikaryotic) belonged to the species Fomes inzengae , while the other isolates corresponded to the species Fomes fomentarius sensu stricto . As far as we know, this is the first record of Fomes inzengae in Belgium. This fungus was also found in a mature tree not showing any signs of decay. This demonstrates its endophytic nature. Growth tests at different temperatures, as well as wood degradation tests in accordance with standard NBN EN113 showed different behavior between both species. Passive sticky traps were installed during two growing seasons at the two sites where F. inzengae had been reported. Spores were detected at all collection times between April and July, using the specific molecular test developed. Moreover, in 2023, the DNA concentrations measured were 100 times higher than in 2022. The implications of this new species in Belgium is discussed in the context of climate change.