The new results on three-pion Bose-Einstein correlations measured with the sample of proton-proton collisions recorded at a centre-of-mass energy of $\sqrt{s} = 7$ TeV are presented, being the first study of three-particle Bose-Einstein correlations in the forward region provided by the LHCb detector. The results are interpreted within the core-halo model for the first time in proton-proton collisions. Together with previous LHCb results on two-pion Bose–Einstein correlation,s measured for the first time in the forward rapidity region at LHC energies, this confirms the observation of collective phenomena in small collision systems. Moreover, the results of the three-particle analysis indicate, for the first time, coherent particle emission.