More: Kremlev footed the bill for hundreds of thousands of dollars of wedding expenses, according to records reviewed by ProPublica and interviews with three people familiar with the event. The oligarch paid to rent out one of the private islands, where a reception was held and where guests slept. He also covered other big-ticket items, like the fireworks show, and his team helped plan the event. Kremlev is the head of the International Boxing Association, a scandal-plagued sports group that has been financed by the Russian state-owned energy giant Gazprom. The wedding payments came from an IBA-affiliated entity in Dubai that the boxing association uses for financial transactions.

Kremlev's previously unreported relationship with Trump Jr. represents an extraordinary development: a member of Putin's circle financially supporting the president's son and gaining intimate access to the Trump family. For a decade, Putin's government, regarded as a chief adversary of the U.S., has been accused of efforts to influence American elections. Attempts by Russia to make inroads with the Trumps before the 2016 election exploded into controversy that dogged much of the president's first term.

In the days leading up to Trump Jr.'s wedding, Kremlev was in China as part of the delegation accompanying Putin, according to Chinese state media. The month before, Putin had bestowed him with a state honor, the Order of Friendship. The Ukrainian government has imposed sanctions on Kremlev personally, citing his closeness to Putin and Russian security services.

It's not clear why Kremlev helped pay for Trump Jr.'s wedding. The men appear to have met only recently. Public reporting suggests Trump Jr. could have afforded it himself, with Forbes recently estimating his net worth at roughly $300 million.