Momo, a border collie from Sudbury who gained viral canine celebrity status, has passed away, his human Andrew Knapp announced Saturday.

The travel-loving Knapp has now produced five books based on Momo and now his new dog, Boo.

The books have a simple concept – Knapp takes photos of Momo (and Boo) hiding in a variety of landscapes, and challenges people to find them.

Momo first went viral on social media (currently more than 600,000 followers on Instagram). Later, Knapp’s 2014 photo book “Find Momo” was featured on the New York Times bestseller list.

For a full photo gallery, head over to Sudbury.com