In "The Fowl Twins"—the first of a series of novels focusing on Artemis's younger twin brothers Beckett and Myles—it is mentioned that Artemis is currently six months into a five-year mission to Mars in a wind-up rocket he built in the family barn. He is accompanied by Butler, but has left his younger brothers Beckett and Myles under the 'guardianship' of NANNI, an artificial intelligence he created, whose voice and mannerisms were based on Holly Short. Holly herself has now been promoted to Commodore and appears at the end of the novel, the narrative observing that a combined grin and grimace is a traditional expression for anyone who spends prolonged time with the Fowls.