The first trefoil leaf-shaped cluster, a novel structural motif, was discovered by quantum chemical computations using density functional theory methods for both binary M-3@E-20 silicon and germanium clusters in which a metallic M-3 cycle is encapsulated within a D-3h Si-20 or Ge-20 cage. The triatomic transition metal Fe-3, Ru-3, and Os-3 cycles exhibit a suitable size to be placed inside both Si and Ge cages and satisfy electronic conditions, which thermodynamically stabilize the mixed clusters. Stabilizing orbital interactions between the M-3 cycle and D-3h, E-20 cage crucially contributes to the high stability of the resulting M-3@E-20 trefoil cluster. The novel trefoil leaf-shaped clusters can be used as building units to create different nanoassemblies.