Two bears who have spent most of their lives side-by-side have finally been allowed to play together for the first time.

Brothers Kai and Riku are two of four brown bears who arrived at the Yorkshire Wildlife Park in Doncaster, U.K., earlier this month.

Park spokesperson Liam Smith said the brothers spent the first 17 years of their lives in a museum in Japan, where their living conditions caught the attention of animal welfare groups.

“They’ve been in fairly small cages, with enough room to just move two steps back and two steps forward,” Smith told “Even though they’ve spent that amount of time next to each other, they’ve never actually been able to interact properly or play with each other.”

According to Smith, the park spent more than a year working with the animal welfare groups and the museums to relocate the bears after determining that no Japanese zoos were willing to take them.

Once the bears arrived at the park, they were kept separate to give them time to get used to their new surroundings and larger homes.

Earlier this week, Kai and Riku started making what Smith describes as “huffing noises” at each other across the fence keeping them apart. The noises were taken as a sign that the bears liked each other and could be brought together.

That happened Wednesday morning, with the brothers first coming into with each other – the first bears they have ever touched – and then being let out into the park’s main nature reserve.

“They were playing, rolling around with each other, kind of playfully biting each other,” Smith said. “It was fantastic. It was really amazing to watch.”

The other two bears who made the 8,500-kilometre-plus trek with Kai and Riku are known as Hanako and Amu. They are older than Kai and Riku.

Park officials say they have also shown early signs of playfulness and happiness, including the “very sassy” Hanako quickly diving into her food and splashing around in water as soon as she arrived at the park and was let out of her crate.

The four bears are all Ussuri brown bears, which are listed as a threatened species by the International Union for Conservation of Nature. They can live for up to 35 years and weigh as much as 550 kilograms.