The Abu Dhabi Investment Council more than tripled the size of its position in a Bitcoin exchange-traded fund during the third quarter, shortly before the bull market in cryptocurrencies gave way to a brutal selloff.

The firm, an independently-run unit of sovereign wealth fund Mubadala Investment Co., increased its holding in BlackRock Inc.’s iShares Bitcoin Trust ETF to almost 8 million shares as of Sept. 30, according to a regulatory filing. The position, disclosed by a subsidiary of ADIC, was worth about $518 million at the time. It held 2.4 million shares three months earlier.