A new recombinant form representing a mosaic of HIV-1 subtype B and F1 and designated as CRF42-BF was identified in Luxembourg. We confirmed the inedited nature of CRF42-BF by near full-length genome characterization and retrieved a possible ancestor originating from Brazil. The demographic history of CRF42-BF in Luxembourg using Bayesian coalescent-based methods was investigated. The exponential phase of the logistic growth happened in a very short time period of approximately 5 months associated with a high mean rate of population growth of 15.02 new infections per year. However, CRF42-BF was not characterized by either a higher ex vivo replication capacity in peripheral blood mononuclear cells (PBMCs) or a higher ex vivo transmission efficiency from monocyte-derived dendritic cells to PBMCs as compared to B and F1 viruses. These data do not support a high pathogenic potential of CFR42-BF but rather an initial bursting spread of the recombinant probably due to a more favorable transmission route.