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We present the serendipitous discovery of the fastest Main Sequencehyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey(S5). The star S5-HVS1 is a $\sim 2.35$ M$_\odot$ A-type star located at adistance of $\sim 9$ kpc from the Sun and has a heliocentric radial velocity of$1017\pm 2.7$ km/s without any signature of velocity variability. The current3-D velocity of the star in the Galactic frame is $1755\pm50$ km/s. Whenintegrated backwards in time, the orbit of the star points unambiguously to theGalactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with avelocity of $\sim 1800$ km/s and travelled for $4.8$ Myr to its currentlocation. This is so far the only HVS confidently associated with the GalacticCentre. S5-HVS1 is also the first hyper-velocity star to provide constraints onthe geometry and kinematics of the Galaxy, such as the Solar motion$V_{y,\odot}= 246.1\pm 5.3$ km/s or position $R_0=8.12\pm 0.23$ kpc. Theejection trajectory and transit time of S5-HVS1 coincide with the orbital planeand age of the annular disk of young stars at the Galactic centre, and thus maybe linked to its formation. With the S5-HVS1 ejection velocity being almosttwice the velocity of other hyper-velocity stars previously associated with theGalactic Centre, we question whether they have been generated by the samemechanism or whether the ejection velocity distribution has been constant overtime.

The Great Escape: Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*