Astrophysical neutrinos are mysterious particles of ultra-high energies with no known progenitor. Since 2011, the IceCube neutrino observatory has been detecting numerous neutrino events with energies of hundreds of TeV. However, it hasn’t been able to pinpoint source for the majority of events. The only exception is IceCube-170922A whose source is believed to be a blazar TXS 0506+056 that was undergoing a flare across the whole electromagnetic spectrum. Despite this association, chance that this is simply a random coincidence was rejected at just 3σ which is not enough to be deemed a discovery. Here we will present results of TXS 0506+056’s rapid optical observations conducted by MASTER-Net telescopes mere minutes after the IceCube trigger that show clear evidence towards it being source of IceCube-170922A.