On 2019 April 25, the LIGO Livingston detector observed a highly significant compact binary coalescence with signal-to-noise ratio 12.9. The component masses were inferred to be between 1.1 and 2.5 solar masses, indicating a likely binary neutron star origin. However, both the total mass and chirp mass are significantly (5 sigma) larger than those of any previously known binary neutron star system. The possibility that one or both binary components of the system are black holes cannot be ruled out from gravitational-wave data. In this talk, I will present the detection of this event, its source properties, and possible origins of the system based on its inconsistency with the known Galactic binary neutron star population.