A 13-year-old missing Shih Tzu has been reunited with his family after eight years of mistreatment and neglect.

The dog, named Watson, disappeared from his family’s home in Hilton, Perth, Australia, in August 2012.

But now, at the ripe old age of 13, the dog was found on Friday, January 8, on the side of the road, having been left there in blistering 41C heat.

He was taken to the vets where his microchip was scanned – bringing up the details of his former owner Sheri Yeoman despite the fact she hadn't seen the pooch in eight years.

“He’s been very good with us at home, having cuddles and being patted by the kids,” owner Sheri Yeoman told 10NEWS.

A photo of Watson before he went missing

“So I think that he knows he is home.”

When he went missing eight years ago, Ms Yeoman and her partner Lee Turner posted thousands of flyers and made countless phone calls to vets and pounds around their home hoping, in vain, to track him down.

Mr Turner believes another family had been keeping Watson as their own.

“It was our understanding that he was passed on from that family to other family members,” he said.

Owner Sheri Yeoman is delighted to have him back

“It was impossible for us to investigate or for police to investigate any further.”

During that time, it is believed Watson, who is now blind and deaf, was neglected and mistreated.

He suffers from eye, skin and ear infections.

“He’s also got a heart murmur. With the condition of his heart at the moment, the vet thinks (Watson has) maybe around six months,” Ms Yeoman said.

Mr Turner said the family would now do the best they could to keep him comfortable so he can “enjoy the time he’s got left”.