The Museum of World War II, located in Natick, has acquired a copy of “Grimm’s Fairy Tales” signed and inscribed “Anne Frank en Margot Frank.” (Margot was Anne Frank’s sister.) The book, and an accompanying letter signed by Otto Frank, the girls’ father, had been valued at between $20,000 and $30,000 by Swann Auction Galleries. In the letter, to a family friend, Otto Frank says the discovery of the book had affected him deeply, explaining that his daughters had left the book behind in the house in Amsterdam where the family stayed before going into hiding. According to the auction house, the sale of this book is the first major offering of Anne Frank material at auction in over 20 years. “Anne Frank is one of, if not the most evocative personages of World War II,” said museum director Ken Rendell. “From an educational standpoint, the book is a fabulous edition to the museum, which already has one of the best Holocaust collections. This is a piece that will add significantly to the experience of the museum.”Names can be reached at email@example.com Follow Mark Shanahan on Twitter @MarkAShanahan.