I'm the Top Crammer at Hogwarts

In 1991, one summer, little Lewis, an old Londoner with the Union Jack in his heart, received his Hogwarts acceptance letter. From then on, the students of Hogwarts were in for a lifelong nightmare. Many years later, when Ms. Hermione Granger, now Minister for Magic, was asked, “What do you think of the Prince of Hogwarts?”, Ms. Granger shuddered. She remembered being swallowed by a mimic chest, chased by a tree sentinel, and riding a roller coaster on the back of Deathwing. At last, a faint smile crossed her face. Those had been their most carefree days. “His Highness the Prince is the greatest alumnus in Hogwarts history,” she and Mr. Potter, Head of the Department of Magical Law Enforcement, answered in unison. Note: The female lead is not Hermione, and the original pairings remain intact.