Kingdom Holding has paid $50 million to double its stake in the microblogging site to 0.72 percent, the Riyadh-based company said in a separate bourse statement.
Prince Alwaleed personally owns 30,100,078 Twitter shares, or 4.45 percent of the company, according to Reuters calculations, accounting for the bulk of the two parties' combined stake.
The statement from the prince's office did not say whether his personal investment in Twitter had changed.
The prince and Kingdom Holding first invested $300 million in Twitter in 2011. Prince Alwaleed owns 95 percent of Kingdom Holding.
Twitter listed on the New York Stock Exchange in November 2013. Its market capitalisation is $18.7 billion, according to Reuters data.