By Valerie Tejeda

"Friends are the family you choose for yourself," is a quote that runs deep for a lot of us. And in a day and age when so many stories are about mean girls, Queen bees, and bad blood, it's refreshing to see how two hugely successful female young adult authors have each other's backs in the best way possible.

Holly Black and Cassandra Clare have been friends for over 10 years. The two first met when Holly was just about to publish her now bestselling series, “The Spiderwick Chronicles;” and Cassandra was working on “City of Bones,” the first book in her widely popular “The Mortal Instruments” series.

They bonded over hot chocolate and shoe shopping, and the rest is basically history. The best part? The two authors live just around the corner from each other. Call it a match made in literary heaven, or the perfect parabati (if you've read Clare's series, you’ll get the reference), but these two ladies are definitely two peas in a pod.

After over a decade of friendship, the authors have finally come together for a middle grade series called “The Magisterium.” The story is set in a world of dark magicians where children train as apprentices to be warriors. It’s a fast-paced fantasy that will definitely leave you wanting more and chomping-at-the-bit for the next installment. “We were just in love with the story and we had to write it together,” Clare told MTV News. Black echoed this sentiment, adding, “We always wanted to work on a book together and this was the right project.”

The first book in the series, “The Iron Trial,” debuted last year and already hit the bestsellers list, and their latest, “The Copper Gauntlet” is also selling like hot cakes. The movie rights have already been sold, and a script is currently in the works.

But what many readers can’t stop talking about is how you would never know the book was written by two people. The consistency of the voice is partly due to the fact that the authors sat next to each other and worked on the book side-by-side.

"I would take the laptop and write 500 words, and then I would hand it to Cassie and she would read it through, edit, and write 500 words,” Black explained. “And then she’d pass it back to me. This was our process throughout the whole book.”

For Black and Clare, working together was easy and natural -- and even the authors themselves can’t tell who wrote what parts in the story. “We always write in the same place and we have to be in the same room,” Clare continued. “We love it. It felt really organic.”

When asked if it was ever difficult at times writing a book together as two hugely successful authors, they both quickly replied with a firm, “No,” saying they brought out the best in each other. “Cassie knows what she wants and she never veers off course,” Black noted. “She’s always true to herself.”

“Holly is very insightful,” Clare continued. “She has an incredible ability to get to the heart of something.”

The authors have also spent many years doing book tours around the world together with readers jumping at the chance to see these two ladies in action. But the common response after going to a Holly Black/Cassandra Clare signing is always, “We love what great friends they are.”

“It helps having each other as a support system,” Clare said. “Women are super supportive of each other. You want what’s best for your friends.”

Holly Black and Cassandra Clare’s “The Copper Gauntlet” is in stores now.