He has a love rival in the form of Grundel Toad, whose mother kidnaps Thumbelina in order for her son to marry Thumbelina. Thumbelina escapes and as Cornelius searches for her, becomes frozen in a pond. He is eventually rescued and fights Grundel Toad just as Thumbelina escapes another suitor, Mr. Mole.
Cornelius and Thumbelina eventually meet up again and get married. Becoming Cornelius' queen allows Thumbelina to become a fairy.