Using femtosecond resolution X-ray solution scattering at a free electron laser we were able to directly observe metal–metal bond cleavage upon photolysis at 400 nm of $Ru_{3}(CO)_{12}$, a prototype for the photochemistry of transition metal carbonyls. This leads to the known single intermediate $Ru_{3}(CO)_{11}(μ-CO)*$, with a bridging ligand (μCO) and where the asterisk indicates an open Ru3-ring. This loses a CO ligand on a picosecond time scale yielding a newly observed triple bridge intermediate, $Ru_{3}(CO)_{8}(μ-CO)_{3}*$. This loses another CO ligand to form the previously observed $Ru_{3}(CO)_{10}$, which returns to $Ru_{3}(CO)_{12}$ via the known single-bridge $Ru_{3}(CO)_{10}(μ-CO)$. These results indicate that contrary to long standing hypotheses, metal–metal bond breakage is the only chemical reaction immediately following the photolysis of $Ru_{3}(CO)_{12}$ at 400 nm. Combined with previous picosecond resolution X-ray scattering data and time resolved infrared spectroscopy these results yield a new mechanism for the photolysis of $Ru_{3}(CO)_{12}$.