UML class diagrams are a relevant modeling language in Software Engineering education since they can be used to teach students how to visualize and display the different entities that compose a system, with their functionalities and relationships. The definition of modeling exercises and their evaluation can be time-consuming for educators due to the need to consider possible semantic variations and alternative representations of the same system requirements. To facilitate teachers in this process, we present TIGRE (auTomated dIagram Generator of REference solutions), an online editor for the definition of UML modeling exercises where teachers can define reference solutions in the form of both diagrams and detailed structures to be used for automated evaluation. The tool is enhanced by the interaction with recent Large Language Models for the automated generation of reference solutions starting from text, facilitating the creation of early drafts. A proof-of-concept case study has been performed by having TIGRE generate reference solutions for two exercises: most of the relevant concepts have been represented correctly, but issues emerged in the form of unnecessary classes being included and incorrect understanding of associations.