Future Harper's author name, H. J. Darling, is a nod towards real life author, J. K. Rowling, author of the Harry Potter Series.
Future Harper, also known in the Series as H.J. Darling, sees that Alex is upset when they first meet. She asks Alex if Mason had broken up with her. This is a reference to the character Mason Greyback (Played by Gregg Sulkin) who makes his first appearance in S3 E8 "Alex Charms a Boy."