A 20-year-old brown bear in Alaska's Katami National Park has been christened a 'supermom' after she adopted a year-old cub abandoned by its mother.

Holly, who is officially known as 'brown bear 435', has already been observed saving the life of a cub with a broken leg in 2007.

The bear with the supercharged maternal instincts, took in the abandoned grizzly when its real mother dumped him at a waterfall this summer after a male bear took more than a passing interest in her.

Supermom: Holly walks through Katami with her adopted cub, (far right) and her own biological cub

Holly, who already was nurturing one cub stepped into the breach and soon her bear-sized altruism was rubbing off on her adopted son, who was seen sharing his own food with his adopted brother.

According to experts this behavior is unusual and almost non-existent between two male bear cubs who are not related.

The abandoned cub is thought to be around 21 months old and was dumped by his mother at Brooks Falls in Alaska in July.

Distraught, the yearling would wait around for his mother to come and collect him, but one day she simply left him for her new mate.

Fishing lessons: The adopted cub (right) faced certain death if Holly had not adopted him after his mother left him

Relaxing: This is the second time in seven years that Holly has adopted a cub left to die by its mother

Park officials who had watched the whole emotionally fraught episode unfold could not intervene and save the bear because of official policy to let nature take its course.

However, when they returned they discovered Holly teaching the cub how to fish.

Holly allowed the cub to join with her and her own offspring and according to Newser and Alaska Dispatch they have become inseparable.

While Holly is obviously saving the life of the cub, experts also believe she could be preserving her own life and cubs too for good measure.