Denver, Colorado - Maximus and Morpheus have been delighting internet users with their doggy antics for years. But when one of the Boerboel brothers passed, the remaining sibling's reaction to his memory broke hearts all over social media.

Five years ago, Maximus was welcomed into the Calton family, alongside his brother Maximus. The two were inseparable and quickly became social media stars, with tens of thousands of followers across multiple platforms.

But this year, tragedy struck. Morpheus died of cancer, leaving his family and Maximus devastated.

A portrait photo of Morpheus went up in the Calton family house, as a tribute to their dearly departed dog.

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Maximus quickly noticed it, and his heartrending reaction was captured in an Instagram video. It shows him staring intently at his late brother's likeness, as well as sleeping under it, instead of his usual spot.

Maximus was hit particularly hard by the loss of his sibling. Days after Morpheus' death, he was still wandering around the house looking for his buddy, and he even refused to eat for four days.

"Devastation is the only word that can come close to how we have felt losing Morpheus," Hilary Calton told Newsweek.

"He was the epitome of the term 'gentle giant.' He was training to be a Children’s Hospital dog, unfortunately, a dream that wasn't able to be fulfilled."

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But Maximus didn't just grieve – he also tried to help his owners deal with the pain.

"When I'm hurting, he seems to sense it in ways that don't require words. That presence alone makes me feel less alone in the middle of this loss," Calton told Newsweek.