A billionaire prince arrested in last week’s corruption crackdown in Saudi Arabia has reportedly sold a key stake in Rupert Murdoch’s 21st Century Fox.

Prince Alwaleed bin Talal was a business partner of media mogul Rupert Murdoch, holding nearly 40-million shares – a 5% stake in the company. The shares that the prince held had special voting rights and enabled the Murdoch family to retain control of the media group.

News that the prince’s $1.5-billion stake has been sold comes just a week before 21st Century Fox’s annual general meeting next Thursday when shareholders will vote on a hostile resolution to get scrap the company’s two-class voting structure. Currently, almost 70% of the company’s issued shares do not entitle holders to a vote.

Murdoch’s control over the family business empire is “looking more uncertain”, according to a report by the Australian Broadcasting Corporation (ABC).

Shareholder activist Stephen Mayne told the ABC Prince Alwaleed had “been the number one backer of Murdoch family control of the public companies for the last 20 years.”

Worth close to $18 billion, Prince Alwaleed is among dozens of royals and former officials arrested in the purge in Saudi Arabia, many of whom are reportedly detained at the Ritz-Carlton Hotel.

The ABC said it was unclear when the shares in Fox and News Corporation were sold and who they have been sold to.

“With his bank accounts and other assets likely to have been frozen by Saudi authorities, his detention had raised questions about who had control over his almost 40 million Fox shares.”

A Bloomberg report on the company’s shareholders showed Prince Alwaleed’s stake fell to zero during this quarter.

In recent years, similar resolutions to change 21st Century Fox’s voting structure have been supported by 30 to 40% of total shares on issue.

“So if those shares are now gone and they are held by normal institutional investors, then the protest vote is likely to be larger than usual at next Thursday’s annual meeting,” Mayne told the ABC.

But he said the prince may have arranged to sell the shares to another shareholder who supported Murdoch retaining control of the group.

“That will probably become clearer after we see the voting results and the debate from Fox Studios in Los Angeles next Thursday.”

Walt Disney Co said this week it had talks with 21st Century Fox about acquiring assets but they failed to agree on a deal. However, analysts say the Murdoch empire is “ripe for other potential suitors“.