Relativistic redshift of the star S0-2 orbiting the Galactic center supermassive black hole

General Relativity predicts that a star passing close to a supermassive black hole should exhibit a relativistic redshift. We test this using observations of the Galactic center star S0-2. We combine existing spectroscopic and astrometric measurements from 1995-2017, which cover S0-2s 16-year orbit, with measurements in 2018 March to September which cover three events during its closest approach to the black hole. We detect the combination of special relativistic- and gravitational-redshift, quantified using a redshift parameter, $Upsilon$. Our result, $Upsilon=0.88 pm 0.17$, is consistent with General Relativity ($Upsilon=1$) and excludes a Newtonian model ($Upsilon=0$ ) with a statistical significance of 5 $sigma$.