Advanced LIGO detected gravitational waves from two coalescing black holes on 14 September 2015.
And we already had really awesome evidence of their existence from binary pulsars.

We now have a large catalogue of gravitational wave candidates from the global LIGO–Virgo–KAGRA detector network. We also have our first multimessenger detection, where the gravitational wave source (two coalescing neutron stars) was also identified by telescopes observing across the electromagnetic spectrum.