Rothschild increased his holding from 21,524,918 shares to 26,714,584 shares, crossing the 14% threshold.
According to an announcement posted to the stockmarket, Rothschild executed the transaction on January 14, roughly a week after the financier delivered an ultimatum to Sir Julian Hornsmith asking the senior independent director to up his response to allegations of financial irregularity or reconsider his post.
A meeting was also called to consider the future of 12 out of 14 Bumi directors, and after increasing his holding Rothschild will have 18.2% of the general meeting vote.
However the resources firm's board has not been quiet on the matter, and after receiving Rothschild's email hit back and urged him to shoulder some of the blame.
'Nat Rothschild's ongoing actions with regard to the company are serving only to distract and delay the board and management further from executing its plan to address the company's issues and maximise shareholder value,' Bumi investors were told, though over the weekend the controversy started to heat up again after chair Samin Tan hinted in emails seen by Reuters he could stand down.
Bumi floated at £10 per share and on Tuesday closed at £3.13.