The gyromagnetic factor of the low-lying E = 251.96(9) keV isomeric state of the nucleus Zr-99 was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of J(pi) = 7/2(+), with a half-life of T-1/2 = 336(5) ns. The isomer was produced and spin aligned via the abrasion-fission of a U-238 primary beam at RIKEN RIBF. A magnetic moment vertical bar mu vertical bar = 2.31(14)mu(N) was deduced showing that this isomer is not single particle in nature. A comparison of the experimental values with interacting boson-fermion model IBFM-1 results shows that this state is strongly mixed with a main nu d(5/2) composition. Furthermore, it was found that monopole single-particle evolution changes significantly with the appearance of collective modes, likely due to type-II shell evolution.