Michael Chernoy, once a powerhouse in Russia's aluminium business, has upped the ante on Oleg Deripaska, the man behind Rusal, in a long-running dispute over ownership of the company.
He has just formally begun proceedings in the UK High Court, alleging that 20% of the company is rightfully his under an agreement allegedly reached with Deripaska in a London hotel in March 2001.
It's far from being the first time Chernoy has made the claim but the move in the UK court system marks a serious escalation and one that seems strategically timed to get in ahead of the three-way merger between Rusal, its Russian sister SUAL and the aluminium interests of Swiss trade house Glencore.
According to the Financial Times, Chernoy is seeking a ruling on the validity of his claim, which would open the way for compensation of up to $3 billion.