Castle's daughter, eighteen-year-old Alexis, is his only child from his first marriage. Alexis is an old soul who is wise beyond her years and never ceases to amaze Castle with her wisdom and insight. She has inherited Castle's charm and wit but rebelled against his devil-may-care attitude about life by being overly practical and methodical about her own. She's honest and loyal to a fault (even in the face of peer pressure) and holds high standards for herself and those she loves.
Sometimes in her relationship with her father, it's difficult to tell which one's the parent and which one's the child. But as she approaches adulthood, Alexis is beginning to challenge her relationship with Castle and isn't afraid to test her limits. It's the time in her life when she needs to figure out who she is and what she wants, even if Castle isn't on the same page. However, she knows that no matter what, whether she fails or succeeds - he will always be there to cheer her on.