Owing to the detection of mixed modes, subgiant and red-giant stars provide a unique opportunity to probe the complete stellar structure of solar-like stars and to constrain stellar structure and evolution models. KIC 11026764 (Gemma) is a subgiant observed for more than 48 months with around 30 detected modes, a perfectly suited benchmark star. Using our recently developed method to analyse mixed-mode spectra, EGGMiMoSA, and aided by our local minimisation code, PORTE-CLES, we search for stellar models adjusting mixed-mode seismic indicators to precisely constrain the structure of Gemma, a milestone in the context of the PLATO mission. Testing different sets of physical parameters, we aim at unveiling Gemma’s convective history. Combining seismic indicators defined in the EGGMiMoSA framework, namely, Δν_0, Δπ_1, and ε_g with spectroscopic observable (T_eff and log g), and testing different chemical compositions and overshooting amounts, we show that while Gemma is expected to be relatively massive (M ~ 1.17 M⊙), solutions without a convective core during its main-sequence phase are favoured.