An intercluster reaction between Au25(PET)18 and Ir9(PET)6 producing the alloy cluster, Au22Ir3(PET)18 exclusively, is demonstrated where the ligand PET is 2-phenylethanethiol. Typical reactions of this kind between Au25(PET)18 and Ag25(SR)18, and other clusters reported previously, produce mixed cluster products. The cluster composition was confirmed by detailed high-resolution electrospray ionization mass spectrometry (ESI MS) and other spectroscopic techniques. This is the first example of Ir metal incorporation in a monolayer-protected noble metal cluster. The formation of a single product was confirmed by thin layer chromatography (TLC). Density functional theory (DFT) calculations suggest that the most favorable geometry of the Au22Ir3(PET)18 cluster is one wherein the three Ir atoms are arranged triangularly with one Ir atom at the icosahedral core and the other two on the icosahedral shell. Significant contraction of the metal core was observed due to strong Ir-Ir interactions.