JPMorgan Chase, the bank that lost at least $5.8bn through a massive credit derivatives position created by a trader nicknamed the “London Whale”, has filed a lawsuit against his boss.

The bank issued a claim in the High Court in London last week against Javier Martin-Artajo, court records show. Mr Martin-Artajo supervised Bruno Iksil, the trader who led the team that was allegedly responsible for the losses, and who was known by the monikers “Voldemort” and the “whale” for his outsize position.

While the bank has filed its claim in court, it has not yet served it upon Mr Martin-Artajo, who will not have an opportunity to file his response until after that stage. This also means no details of the bank’s arguments are publicly available. The bank has up to four months to serve its claim.