Fans of young adult novels saw their favorite worlds collide early Tuesday morning when "Harry Potter" author J.K. Rowling responded to a tweet by "The Fault In Our Stars" author John Green.

Rowling recently started following Green, and the latter wondered aloud to his 3.46 million followers if the British writer might see his tweets about the Cyber Monday sale happening on his website, DFTBA.com (which stands for "Don't Forget to Be Awesome"). The site sells merchandise that references pop culture including the "Harry Potter" universe.

"(It occurs to me that new follower JK Rowling might see tweets about the DFTBA sale, which is odd, but, whatever, EVEN ICONS NEED T-SHIRTS.)" he tweeted late Monday night.

When Rowling awoke on Tuesday morning, she came across the tweet and responded with a tweet every Potterphile would appreciate.

.@johngreen I own one that says 'Horcruxes Got Soul' but I don't wear it out much," she wrote.

A Horcrux is powerful object used by Dark wizards or witches in the "Potter" books to attain immortality by anchoring his or her soul to the earth if the body is destroyed.

DFTBA was created by Green and his brother Hank, who also host the YouTube channel VlogBrothers.