The standard neutrino oscillation parametrization is defined by six independent parameters: three mixing angles (θ23, θ12 and θ13), two squared mass differences and a CP violation phase (δcp). By 2010, only θ13 and δcp were still unknown. Despite the non-zero measured values of θ12 and θ23, a non zero value of θ13 is also necessary to open the window to explore CP violation on the lepton sector. In 2011, T2K (accelerator based) and Double Chooz (reactor based) experiments showed an evidence of non-zero θ13. Nowadays, it is measured with a 3.4% error, lead by the Daya Bay reactor experiment. θ13 is today one of the most precisely known mixing angles. However, with the next generation of experiments, such as JUNO, DUNE and HK, it will become the least precise mixing angle. In this seminar, I shall review the past and present θ13 measurement status that I have witnessed for the past decade. In addition, I will highlight for the first time a possible novel approach for improving the precision of θ13 to the sub-percent range, that is considered unattainable with any current techniques, including planned experiments under construction. This unprecedented level of uncertainty will allow the neutrino PMNS mixing matrix to be constrained within the sub-percent level, thus opening for a direct new precision test of the Unitarity in neutrino physics.