The second child of Royal Druid Declan ó Broin, Tadhg was originally born to a poor Seelie woman living in Sgíreil. He was born extremely premature, with many health issues, including albinism, blindness, and malformed wings. Because of this, he was eventually surrendered to the Royal Orphanage system. When he was 3 years old, he was adopted by the Royal Druid.
Growing up, Tadhg was very close with his sister, Zabelle, who taught him much of what he knows about magick. However, after she left the country in 2016, he was forbidden from communicating with her, and seems to have become much closer with his father.