DUBAI, May 22 (Reuters) - Saudi billionaire Prince Alwaleed bin Talal has signed an agreement with Saudi Arabia's powerful sovereign wealth fund to sell 16.87% of his investment firm Kingdom Holding Co to the fund, the company said on Sunday.

The Public Investment Fund (PIF) will buy 625 million shares at 9.09 riyals ($2.42) a share, Kingdom Holding said in a stock exchange filing, for a total of 5.68 billion riyals ($1.51 billion).

The share price for the agreement was where the stock closed on Thursday, its lowest level in a year. It rallied 8.8% to 9.89 riyals by 0802 GMT on Sunday.

Prince Alwaleed was swept up in an anti-corruption campaign ordered by the crown prince in 2018. He was held for about three months at Riyadh's Ritz-Carlton, along with scores of royals, senior officials and businessmen.

In March 2018, he said he reached a "confidential and secret" settlement with the Saudi government. Most detainees were released after reaching financial settlements that netted just over $100 billion for the state, the attorney general said at the time, without providing further details.

The PIF did not immediately respond to emailed requests for comment.

Asked if the transaction was related to the settlement, a spokesperson for Prince Alwaleed said it was "purely a business deal", declining to comment further.

The transaction will take place on Saudi Arabia's stock exchange, Tadawul, on Sunday, the company said. Prince Alwaleed, one of the kingdom's most recognised business figures, will retain a majority 78.13% stake.

The PIF, which manages over $600 billion in assets, is at the centre of Saudi Arabia's de facto ruler Crown Prince Mohammed bin Salman's ambitious agenda to diversify the economy away from oil.

The investment firm said in a separate filing on Sunday that one of its executive directors, Sarmad Zok, had resigned. Abdulmajeed Ahmed Al-Hagbani will replace him on the board, as a non-executive director. Hagbani is a senior director at PIF, according to LinkedIn. ($1 = 3.7510 riyals) (Reporting by Yousef Saba;Editing by Elaine Hardcastle)