tnk-bp became russia's third largest oil company. in 2013 tnk-bp was sold to rosneft for us$56 billion, a sale described by "reuters" as "one of the biggest energy takeovers in history." khan joined mikhail fridman in establishing letterone, based in luxembourg, for the purpose of investing some of the proceeds from the tnk-bp sale in international projects. letterone's l1 energy fund was founded in 2013. khan has donated funds to non-profits such as the european jewish fund, and co-founded and supports the genesis philanthropy group.