Complex sentence: After three years, and against the wishes of his mother, he left this tedious occupation and resumed his studies at the Academy, studying under Théodore-Joseph Canneel and Julius De Keghel.
Split into simpler sentences: After three years, and against the wishes of his mother, he left this oppressive occupation and resumed his studies at the Academy. His teachers were then Théodore-Joseph Canneel and Julius De Keghel.