Following the discovery of dimethyl sulfide (DMS; CH3SCH3) signatures in comet 67P/Churyumov-Gerasimenko, we report the first detection of this organosulfur species in the interstellar medium during the exploration of an ultradeep molecular line survey performed toward the Galactic center molecular cloud G+0.693-0.027 with the Yebes 40 m and IRAM 30 m telescopes. We derive a molecular column density of N = (2.6 +/- 0.3) x 1013 cm-2, yielding a fractional abundance relative to H2 of similar to 1.9 x 10-10. This implies that DMS is a factor of similar to 1.6 times less abundant than its structural isomer CH3CH2SH and similar to 30 times less abundant than its O-analog dimethyl ether (CH3OCH3) toward this cloud, in excellent agreement with previous results on various O/S pairs. Furthermore, we find a remarkable resemblance between the relative abundance of DMS/CH3OH in G+0.693-0.027 (similar to 1.7 x 10-3) and in the comet (similar to 1.3 x 10-3). Although the chemistry of DMS beyond Earth has yet to be fully disclosed, this discovery provides conclusive observational evidence on its efficient abiotic production in the interstellar medium, casting doubt on using DMS as a reliable biomarker in exoplanet science.