Question: Who's the husband of the writer of The Unknown?

full_context: Document 1: The Secret Series: The Secret Series is a series of 'secret'-themed adventure novels written by Pseudonymous Bosch, who is suspected to be Raphael Simon. The series centers on three middle school children, Cass, Max-Ernest, and Yo-Yoji, and their adventures as members of the Terces Society ("secret society" spelled backwards), a group that keeps a mysterious Secret from being found out or stolen by the Midnight Sun society. One of the subplots of the series is the alchemists of the Midnight Sun searching for the secret to immortality, and the Terces Society's plans to stop them.
Document 2: Animorphs: Animorphs is a science fantasy series of young adult books written by Katherine Applegate and her husband Michael Grant, writing together under the name K. A. Applegate, and published by Scholastic. It is told in first person, with all six main characters taking turns narrating the books through their own perspectives. Horror, war, dehumanization, sanity, morality, innocence, leadership, freedom and growing up are the core themes of the series.
Document 3: The 39 Clues: The 39 Clues is a series of adventure novels written by a collaboration of authors, including Rick Riordan, Gordon Korman, Peter Lerangis, Jude Watson, Patrick Carman, Linda Sue Park, Margaret Peterson Haddix, Roland Smith, David Baldacci, Jeff Hirsch, Natalie Standiford, C. Alexander London, Sarwat Chadda and Jenny Goebel. It consists of five series, "The Clue Hunt", "Cahills vs. Vespers", "Unstoppable", "Doublecross", and recently released, "Superspecial". They chronicle the adventures of two siblings, Amy and Dan Cahill, who discover that their family, the Cahills, has been the most influential family in history. The first story arc concerns Dan and Amy's quest to find the 39 Clues, which are ingredients to a serum that can create the most powerful person on Earth. This series' primary audience is age 8–12. Since the release of the first novel, "The Maze of Bones", on September 9, 2008, the books have gained popularity, positive reception, and commercial success. s of 2010 , the book series has about 8.5 million copies in print and has been translated into 24 languages. The publisher of the books is Scholastic Press in the United States. Steven Spielberg acquired film rights to the series in June 2008, and a film based on the books was set to be released in 2016 but production has not yet started as of August 2017. The series also originated tie-in merchandise, including collectible cards and an interactive Internet game.
Document 4: The Power of Five: The Power of Five (also known as The Gatekeepers in the US) is a series of five fantasy and suspense novels, written by English author Anthony Horowitz and published between 2005 and 2012. It is an updated re-imagining of Horowitz's "Pentagram" series, which the author had left unfinished in the 1980s. The series is published in the United Kingdom by Walker Books Ltd and in the United States by Scholastic Press. The novels deal heavily in the occult and examples of things such as human sacrifice and blood rituals are major plot elements, such as in the first book, where Matthew Freeman is hunted by a Cult who want to conduct a blood sacrifice on him to blast open a portal using a combination of nuclear physics and black magic, to unlock another dimension which is holding a group of ancient evil demons captive.
Document 5: Doom novels: The "Doom" novel series is a series of four near-future science fiction novels co-written by Dafydd ab Hugh and Brad Linaweaver; "Knee-Deep in the Dead", "Hell on Earth", "Infernal Sky", and "Endgame". The series is initially based on the "Doom" and "" first-person shooter video games created by Id Software, although there are multiple departures from the game in the first two novels, and the second two continue in an independent direction to the games' storylines. The novels are primarily written from the first-person perspective of Flynn Taggart, a corporal assigned to Fox Company of United States Marine Corps, although the perspective changes from character to character in the second and third novel.
Document 6: The Survivor (Mills novel): The Survivor is the fourteenth novel in the Mitch Rapp series. It was published on October 6, 2015. It is the first novel in the series to be written by Kyle Mills, after the death of previous series author, Vince Flynn.
Document 7: Son (novel): Son is the final entry in "The Giver Quartet" by Lois Lowry. It was preceded by "Messenger", the third book of the series. The book follows Claire, the mother of Gabriel, the baby seen in "The Giver".
Document 8: The Unknown (novel): The Unknown is the 14th book in the Animorphs series, written by K.A. Applegate. It is narrated by Cassie. The front cover quote is, "Never underestimate the power of a morph...". All books after "The Unknown" were dedicated to Applegate's son, Jake, as well as her husband and co-writer, Michael.
Document 9: The Attack (novel): The Attack is the 26th book in the Animorphs series, written by K.A. Applegate. It has the distinction of being the last book in the series written by Applegate on a regular schedule; with "The Separation", the final two books in the regular series; "The Answer" and "The Beginning", two Megamorphs books; "Elfangor's Secret" and "Back to Before", and the chronicles; "Visser", and "The Ellimist Chronicles" being the only other Animorphs related books written by her after this was published. It is narrated by Jake.
Document 10: K. A. Applegate: Katherine Alice Applegate (born October 9, 1956 in Ann Arbor, Michigan) is an American young adult and children's fiction writer, best known as the author of the "Animorphs", "Remnants", "Everworld", and other book series. She won the 2013 Newbery Medal for her 2012 children's novel "The One and Only Ivan". Applegate's most popular books are science fiction, fantasy, and adventure novels. She won the Best New Children's Book Series Award in 1997 in "Publishers Weekly". Her book "Home of the Brave" has won two awards. She also wrote a chapter book series in 2008-9 called "Roscoe Riley Rules".
Document 11: The Baby-Sitters Club: The Baby-Sitters Club (also known as BSC) is a series of novels written by Ann M. Martin and published by Scholastic between 1986 and 2000, that sold 176 million copies. Martin wrote the first 35 books in the series, but the subsequent novels were written by ghostwriters, such as Peter Lerangis and many uncredited others.
Document 12: Michael Grant (author, born 1954): Michael Grant (born July 26, 1954) is an American author of young adult fiction. He has written over 150 books, though most are as a co-author with his wife. Together they have written the "Animorphs" and the "Everworld" book series, as well as the "Making Out" book series. Grant is the sole author of the "Gone" Series, "BZRK, the Messenger of Fear Series a"nd has a new series, the first of which is called ""Front Lines"", publishing in January 2016. ""Front Lines"" was originally called ""Soldier Girl"."
Document 13: Time Quintet: The Time Quintet is a fantasy/science fiction series of five young adult novels written by Madeleine L'Engle.
Document 14: The Giver Quartet: The Giver Quartet is a series of four young adult novels by Lois Lowry. The quartet consists of "The Giver" (1993), "Gathering Blue" (2000), "Messenger" (2004) and "Son" (2012). The first book won the 1994 Newbery Medal and has sold more than 10 million copies. The story takes place in the world of the Giver. Each book has a different protagonist, but is set in the same futuristic era.
Document 15: The Solution (novel): The Solution is the 22nd book in the Animorphs series, written by K.A. Applegate. It is narrated by Rachel. It is the last book in the David trilogy.
ground_truth: Michael Grant