In the title mol-ecule, C(28)H(28)O(9), the phenol and the benzene rings adjacent to the α,β-unsaturated ketone unit are inclined at 9.15 (13)° to each other. The terminal phenyl ring is oriented with respect to the phenol ring at a dihedral angle of 85.88 (13)°. In the crystal, the methyl-ene C atoms of the dihydro-dioxine ring are disordered over two sites with an occupancy ratio of 0.463 (18):0.537 (18), and both disordered components of the dihydro-dioxine ring adopt twisted-chair conformations. An intra-molecular O-H⋯O hydrogen bond and weak inter-molecular C-H⋯O hydrogen bonds are present in the crystal structure.