© 2016 American Physical Society. The η′ transition form factor is reanalyzed in view of the recent first observation by BESIII of the Dalitz decay η′→γe+e- in both space- and timelike regions at low and intermediate energies using the Padé approximants method. The present analysis provides a suitable parametrization for reproducing the measured form factor in the whole energy region and allows one to extract the corresponding low-energy parameters together with a prediction of their values at the origin, related to Γη′→γγ, and the asymptotic limit. The η-η′ mixing is reassessed within a mixing scheme compatible with the large-Nc chiral perturbation theory at next-to-leading order, with particular attention to the Okubo-Zweig-Iizuka-rule-violating parameters. The J/ψ, Z→η(′)γ decays are also considered and predictions are reported.