A Los Angeles woman named Mackenzie Coffman noticed that her cat, Simon, spent a lot of time staring back and forth with a neighbor’s cat through their apartment windows. She decided to formally introduce Simon to the cat across the way by making a sign.

Shortly thereafter, a sign appeared in the other cat’s window, introducing him as Theo. Mackenzie and her neighbor even opened their windows so the cats could “talk.”

Eventually, they met. When Simon visited Theo, he got scared and hid under a sofa. His patient new friend went and sat with him.

When Theo visited Simon’s apartment, on the other hand, all Simon wanted to do was play with his pal, who needed some time to adjust to his new surroundings.

Both cats have gained large followings on Twitter, where they post adorable updates about their growing friendship. You can follow Simon at @lovesimoncat and Theo at @Theothecat5.