Prince Alwaleed bin Talal, the richest man in the Arab world, has increased his Kingdom Holding Company's share stake in Twitter to become the social media giant's second largest shareholder.

The ostentatious Saudi royal and Kingdom Holdings increased their ownership in the past six weeks to a total of 34,948,975 shares, representing more than 5% of Twitter's common stock. The shares have a market value of $1bn (£653m, €888m), the company said in a statement. The billionaire prince's company originally invested $50m in the tech company in 2011, doubling its stake since August.

In July, Bin Talal the grandson of King Abdul-Aziz Alsaud, the founder and first ruler of Saudi Arabia, made headlines when he announced he would give his $32bn fortune to charity when he dies. He has not been a silent investor in Twitter and has criticised CEO Jack Dorsey, who he said should return to his job running mobile payments company Square.

Aside from his extravagant wealth and ostentatious philanthropy, the Saudi prince is an anomaly in Saudi Arabian society and the family that rules the country. His best-known charitable gesture is one he regretted suggesting. He made headlines for the wrong reasons in April, when he promised to buy Bentleys for Saudi pilots who had taken part in the air bombing of Yemen.

Unlike his siblings, Bin Talal holds no government position and has dedicated his life to generating staggering amounts of money and, latterly, giving it away.

In 1979, Bin Talal formed Kingdom Establishment for Commerce and Trade, the company that would, in 1996, become Kingdom Holding Company. His first investments were in property in Riyadh, and in 1988 the company acquired a controlling stake in the ailing United Saudi Commercial Bank (USCB).