  We propose a supersymmetric SU(5) GUT model with an A_4 family symmetry -
including a full flavon- and messenger sector - which realises the relation
theta_13^PMNS \simeq theta_C / sqrt(2). The neutrino sector features
tri-bimaximal mixing, and theta_13^PMNS \simeq theta_C / sqrt(2) emerges from
the charged lepton contribution to the PMNS matrix, which in turn is linked to
quark mixing via specific GUT relations. These GUT relations arise after GUT
symmetry breaking from a novel combination of group theoretical Clebsch-Gordan
factors, which in addition to large theta_13^PMNS lead to promising quark
lepton mass ratios for all generations of quarks and leptons and to m_s / m_d =
18.95_(-0.24)^(+0.33), in excellent agreement with experimental results. The
model also features spontaneous CP violation, with all quark and lepton CP
phases determined from family symmetry breaking. We perform a full Markov Chain
Monte Carlo fit to the available quark and lepton data, and discuss how the
model can be tested by present and future experiments.
