The single laser flash photolysis (FP) of 2-(4-benzoylphenyl)-2-phenyl-1-methylenecyclopropane gave rise to a ground state trimethylenemethane (TMM) biradical with absorption bands at 362 and 545 nm and an excited state of this biradical that displays triplet-triplet fluorescence at 580 nm. The excited biradical is likely formed via an expected two-photon process as well as an unexpected one-photon process. The fluorescence quantum yield of the excited biradical, 0.021, was successfully determined by employing a two-color two-laser FP technique.