We report the discovery of a 75 ^ { \circ } long stellar stream in Gaia DR2 catalog , found using the new STREAMFINDER algorithm .
The structure is probably the remnant of a now fully disrupted globular cluster , lies \approx 3.8 { kpc } away from the Sun in the direction of the Galactic bulge , and possesses highly retrograde motion .
We find that the system orbits close to the Galactic plane at Galactocentric distances between 4.9 and 19.8 { kpc } .
The discovery of this extended and extremely low surface brightness stream ( \Sigma _ { G } \sim 34.3 { mag arcsec ^ { -2 } } ) with a mass of only 2580 \pm 140 { M _ { \odot } } , demonstrates the power of the STREAMFINDER algorithm to detect even very nearby and ultra-faint structures .
Due to its proximity and length we expect that Phlegethon will be a very useful probe of the Galactic acceleration field .