The Alien Next Door (8-book series)
by A.I. Newton
illustrated by Anjan Sarkar
Recommended Ages: 6+
While each book stands somewhat on its own on the scale of an elementary-level chapter book, the whole series also works together as a continuous story with each individual book as a kind of chapter in it. My father, who got to it before me, read all eight books in one sitting, and was the first to complain that the last one ends abruptly without really resolving the storyline. Actually, his exact words were, "It just goes pbpbpbpbt." I myself managed it in two settings, but they went quickly in terms of total time. I'm glad to report that according to Fantastic Fiction, a ninth book titled The Marvelous Museum is supposed to come out in October 2022. So, I guess this series isn't over yet.
As for the eight books so far, most of them came out in quick succession in 2018 and 2019 and have charming illustrations, featuring an apparently American (or maybe Canadian?) boy named Harris who begins to suspect that the awkward, lonely new kid next door may actually be an alien from outer space. The more sure of this he becomes, the more his family and his best friend, Roxy, think he's just being mean because Zeke is different. But Harris is right; and after the first couple of books, he and Zeke become friends and Harris begins to share in his secret. Harris and Roxy help Zeke learn about such strange human customs as scouting campouts, trick-or-treating, baseball and Valentines.
Then Zeke finds out his parents, Xad and Quar, have finished their research on Earth and they have to move back to the planet Tragas. At first, Harris and Zeke look for a way to delay their departure. In the last book (so far), Harris reveals Zeke's secret to Roxy, and the two of them stow away on the ship and get to experience the "new kid" phenomenon from the other side, disguised as aliens on a strange new world.
A.I. Newton is also the author of the "Little Olympians" series, also illustrated by Sarkar, in which kid-sized Greek gods go to camp to learn how to use their powers and get along together. Their titles, up to the most recent release, are Zeus, God of Thunder; Athena, Goddess of Wisdom; Hermes, the Fastest God; and Artemis, the Archer Goddess. I can't actually find any information online about A.I. Newton as a human being. For all I know, he may be a fictitious pen-name, maybe with a whole list of author credits under another name.
About illustrator Anjan Sarkar, I've learned that he's a British illustrator of Indian heritage who has contributed art to such books as Rum Pum Pum by David L. Harrison and Jane Yolen, Queen of the Hanukkah Dosas by Pamela Ehrenberg, and Level Up! Last One Standing by Tom Nicoll, among 20-some books.