In 2022, Castle self-published his debut book,
Pringle & Finn, a children's picture book about two male penguins getting married. The book is inspired by Castle's own wedding and the illustrations on his wedding invitations. The book's main characters returned in his 2023 book,
The Secret Ingredient, which shares the penguins' story of becoming parents
. Due to the books' inclusion of gay characters, Castle has stated they have been subjected to book bans. While many on social media increased their support of Castle after hearing about the bans, some questioned whether the books had been banned due to their inclusion of gay characters or if they had been rejected from bookstores because they are self-published. In 2024, he self-published the children's picture book
Adoroscopes, about
horoscopes. == Personal life ==