Warren Buffet is stepping down as a trustee of the Bill & Melinda Gates Foundation less than two months after the couple stated that they planned to divorce, as the multibillion-dollar charity looks to reshape its leadership structure.People familiar with the matter stated that Mr. Buffett’s decision to step down is tied to the foundation’s plans to strengthen its governance and add more independence. Buffett and Gates are longtime friends. Together with Ms. French Gates, they were the foundation’s three trustees. Unlike most large charitable organizations, the foundation doesn’t have a board of directors.Mr. Buffett, the 90-year-old chairman, and chief executive of Berkshire Hathaway Inc., had served as a trustee of the foundation since 2006 when the billionaire pledged to donate all of his company stock to philanthropy. The Gates Foundation is one of the beneficiaries of Mr. Buffett’s generosity.Executives at the charity are currently in the midst of planning for changes because of the Gateses’ impending divorce and what it will mean for the foundation’s $49.9 billion endowments. The Wall Street Journal reported last month that Mr. Gates and Ms. French Gates are discussing changes to the structure of their foundation to apply more governance and independence. The billionaires, who have jointly led the Bill & Melinda Gates Foundation for roughly two decades, are discussing bringing in outside directors, the Journal reported.