Beijing (CNN) China and North Korea boast an alliance forged in blood -- more than 130,000 Chinese troops, including the son of Mao Zedong, died defending the North during the Korean War -- but the relationship has always been an uneasy one.

While Pyongyang is dependent on Beijing for trade and diplomatic support, experts say the North Korean regime has always resented playing the little brother role to the much bigger China.

Now, as North Korean ruler Kim Jong Un establishes himself on the world stage and prepares for summits with South Korean President Moon Jae-in and US President Donald Trump, Beijing fears Pyongyang is moving out of its orbit and striking out on its own.

While China's economic pressure has been pivotal in bringing Kim to the negotiating table, Beijing worries Kim might now agree to a deal that brings his country closer to its old enemies and further from its traditional ally, which has seen it through famine and global isolation.

"There is even an extreme concern within the strategic Chinese community that maybe the US will accept a nuclear capable North Korea as its ally, or at least a friendly country," said Tong Zhao, a nuclear policy expert at Tsinghua Carnegie Center for Global Policy in Beijing.

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