Differences in both stable and labile state variables are known to affect the emergence and maintenance of consistent inter-individual behavioural variation (animal personality or behavioural syndrome), especially when experienced early in life. Variation in environmental conditions experienced by gestating mothers (viz. non-genetic maternal effects) are known to have significant impact on offspring condition and behaviour, yet, their effect on behavioural consistency is not clear. Here, by applying an orthogonal experimental design, we aimed to study if increased vitamin D₃ content in maternal diet during gestation (vitamin-supplemented vs. vitamin control treatments) combined with corticosterone treatment (corticosterone-treated vs. corticosterone control treatments) applied on freshly hatched juveniles had an effect on individual state and behavioural consistency of juvenile Carpetan rock lizards (Iberolacerta cyreni). We tested the effect of our treatments on (i) climbing speed and the following levels of behavioural variation: (ii) strength of animal personality (behavioural repeatability), (iii) behavioural type (individual mean behaviour) and (iv) behavioural predictability (within-individual behavioural variation unrelated to environmental change). We found higher locomotor performance of juveniles from the vitamin-supplemented group (42.4% increase), irrespective of corticosterone treatment. While activity personality was present in all treatments, shelter use personality was present only in the vitamin-supplemented × corticosterone-treated treatment and risk-taking personality was present in corticosterone control treatments. Contrary to our expectations, behavioural type was not affected by our treatments, indicating that individual quality can affect behavioural strategies without affecting group-level mean behaviour. Behavioural predictability decreased in individuals with low climbing speed, which could be interpreted as a form of anti-predator strategy. Our results clearly demonstrate that maternal diet and corticosterone treatment have the potential to induce or hamper between-individual variation in different components of boldness, often in interactions.