Assuming the Riemann Hypothesis (RH), Montgomery (1973) proved a theorem concerning the pair correlation of nontrivial zeros of the Riemann zeta-function. One consequence of this theorem was that, under RH, at least 2/3 of the zeros are simple. We show that this theorem of Montgomery holds unconditionally. In an earlier paper, as an application, under a much weaker hypothesis than RH that all the zeros lie within a narrow vertical box centered on the critical line, we showed that at least 61.7% of zeros of the Riemann zeta-function are simple. We can further weaken the hypothesis using a density hypothesis. Recently we were able to improve a little bit on this proportion, and furthermore found a connection to finding proportion of zeros on the critical line. Inspired by a recent preprint of J. Maynard and K. Pratt, we can additionally weaken our assumption by copying the box finitely many times. This is joint work with Siegfred Alan C. Baluyot, Daniel Alan Goldston, and Caroline L. Turnage-Butterbaugh.