Berkshire Hathaway, the conglomerate led by billionaire investor Warren Buffett, has revealed that it has been accumulating shares of insurer Chubb Ltd. in recent quarters. According to a regulatory filing on Wednesday, Berkshire Hathaway held over 25.9 million shares of Chubb as of March 31, valued at $6.7 billion. The news caused Chubb’s shares to rise more than 8% in after-hours trading. In previous filings, Berkshire Hathaway had been granted permission to keep the details of its holdings confidential, but it has now amended those filings to disclose its stake in Chubb. This stake represents 2% of Berkshire Hathaway’s portfolio. During Berkshire’s annual meeting on May 4, Buffett was not asked about the mystery holding, but it was revealed that the company had reduced its holdings of Apple Inc. and completely sold its stake in Paramount Global at a loss. Despite the reduction, Apple remains Berkshire Hathaway’s largest holding, making up around 40% of its portfolio. Buffett stated that he expects Apple to remain the largest holding at the end of the year.