Gunther, 19, was runner-up to Williams F1 newcomer and Prema teammate Lance Stroll in F3 last year, and was signed by Mercedes' DTM branch as a test and reserve driver. He'd joined Prema from Mucke, having raced for the Berlin-based outfit in German entry-level series ADAC Formel Masters, where he was runner-up in two successive campaigns, and the 2015 edition European F3.