In a series of royal decrees carried on the state-run Saudi Press Agency, the monarch stripped Prince Mohammed bin Nayef, who had been positioned to inherit the throne, from his title as crown prince and from his powerful position as the country's interior minister overseeing security.
The newly announced Crown Prince Mohammed bin Salman already oversees a vast portfolio as defense minister and head of an economic council tasked with overhauling the country's economy.
The young prince was little known to Saudis and outsiders before Salman became king in January 2015. He had previously been in charge of his father's royal court when Salman was the crown prince.
The Saudi monarch, who holds near absolute powers, quickly awarded his son expansive powers to the surprise of many within the royal family who are more senior and more experienced than Mohammed bin Salman, also known by his initials MBS.
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The Allegiance Council is a body made up of the sons and prominent grandsons of the founder of the Saudi state, the late King Abdul-Aziz, who vote to pick the king and crown prince from among themselves.
Over the weekend, the king had issued a decree restructuring Saudi Arabia's system for prosecutions that stripped Mohammed bin Nayef of longstanding powers overseeing criminal investigations, and instead ordered that a newly- named Office of Public Prosecution and prosecutor report directly to the monarch.
The prince had appeared to be slipping from public eye as his nephew, Mohammed bin Salman, embarked on major overseas visits, including a trip to the White House to meet President Donald Trump in March.
That visit to Washington helped lay the foundation for Trump's visit to Saudi Arabia in May, which marked the president's first overseas visit and which was promoted heavily by the kingdom as proof of its weight in the region and wider Muslim world.
The warm ties forged between Riyadh and Washington under the Trump administration may have helped accelerate Mohammed bin Salman's ascension as crown prince.
Despite his ambitions, which include overhauling the kingdom's economy away from its reliance on oil, the prince has faced failures and strong criticism for the Saudi-led war in Yemen, which he oversees as defense minister.
The war, launched more than two years ago, has failed to dislodge Iranian-allied rebels known as Houthis from the capital, Sanaa, and has had devastating effects on the impoverished country.
The US already is helping the Saudis with intelligence and logistical support for the bombing campaign in Yemen, and the Trump administration has signaled it could assist with greater intelligence support to counter Iranian influence there.