The present study investigates the potential of ChatGPT as an L2 teaching support and aims to explore the extent to which this Generative AI-powered tool is helpful for English as a Foreign Language (EFL) teachers. Therefore, this exploratory single instrumental case study followed an EFL teacher using ChatGPT for seven months, from January to June 2023, as an aid for her English classes in a private language school in Spain. Data was collected from her ChatGPT history in relation to her prompting tasks, from outputs received from her lesson plans when she implemented ChatGPT in class, and from a semi-structured post-interview. The analysis followed a qualitative approach using thematic analysis of the data to identify the type of support received by ChatGPT and to determine the level of reliability and helpfulness of the outputs. The results indicate that ChatGPT offers significant support to EFL teachers in planning and designing lessons, and implementing ChatGPT in lessons and assessing learner's writing. Our data highlights the potential of ChatGPT as a support for EFL teachers as long as they possess specific AI competencies, such as prompt crafting to obtain useful and meaningful outputs, and critical thinking, together with EFL teaching knowledge, to recognize inaccuracies and identify relevant outcomes.