Age-metallicity relation for Fornax field stars within the two distinct fields of our study. Left: south-Western field centred at , Right: north-Eastern field centred at . The observed differences between the AMR of Field 1 and 2 are most likely due to small zero-point variations in the photometry (see text). Symbol sizes in both panels reflect the statistical precision of the photometry and [Fe/H], where larger symbols indicate a better quality. Symbols with a right-handed arrow label additional stars with −3.0 ≤ [Fe/H] ≤ − 2.5, which fell outside the lower isochrone range and for which we adopted [Fe/H] = −2.5 to derive lower age limits. Blue symbols highlight stars which we identified as members of the GC H2 (left panel) and H5 (right panel), respectively. The dotted blue line in both panels shows the model prediction for the best fitting SFH from Hendricks et al. (2014), when we assume the age of Fornax to be 13.3 Gyr. While stars from Field 2 appear systematically younger than the model, the AMR from Field 1 shows excellent agreement with the predicted sequence. In contrast, in order to obtain a reasonable fit for Field 2, Fornax could not be significantly older than 10 Gyr, a scenario which can be ruled out from previous photometric and spectroscopic age estimations. From the well populated AMR of Field 1, we find a fast enrichment in [Fe/H] until ~ 8 Gyr ago, after which the enrichment becomes extremely shallow so that a wide range of ages accumulate at [Fe/H] ≈ − 1.0. Finally the chemical enrichment seem to steepen again for stars younger than 4 Gyr, indicating a sudden increase in SF activity at this time.