(Bloomberg) -- When Saudi Arabia announced last week a $20-billion investment in a U.S. infrastructure fund managed by Blackstone, many noticed that it came shortly after presidential son-in-law Jared Kushner personally negotiated a $110-billion arms sale to the country. What went unnoticed — and is largely unknown — is how important Blackstone is to the Kushner family company.

Since 2013, Blackstone has loaned more than $400 million to finance four Kushner Cos. deals — two of which have not been reported — making it one of the business's largest lenders. And their ties go beyond the loans. Stephen Schwarzman, Blackstone's co-founder and CEO, heads Trump's business-advisory council and was in Riyadh with the president and Kushner. The Saudi promise to invest in Blackstone's fund drove the firm's stock up more than 8%.

A Blackstone spokeswoman, Christine Anderson, said the company began talks with the Saudis a year ago, "well before President Trump was even his party's nominee." Blackstone is one of the largest non-bank real-estate lenders, and corporate deals are often announced during state visits. A spokesman for Kushner Cos. declined to comment.

But the sequence of the deals and the intertwined personal relationships of the principals raise concerns about conflicts of interest. Schwarzman, one of the world's richest businessmen, is a Republican and, like Trump, a resident of New York and Palm Beach. Ivanka Trump, the president's daughter and Kushner's wife, was an investor in a fund Blackstone created in 2010 to seed hedge funds, according to financial disclosures.

Kushner has divested some of his assets to family members, and the White House says he'll recuse himself when necessary. (Separately, the Washington Post reported in an unrelated matter Thursday, citing people familiar with the investigation, that Kushner is now a subject of the FBI probe into possible Russian collusion with the Trump campaign. Jamie Gorelick, an attorney for Kushner, told the Post that her client has cooperated with a congressional investigation into the matter and "will do the same if he is contacted in connection with any other inquiry.")

ADVISORY PANEL

Schwarzman's advisory panel — which also includes General Motors CEO Mary Barra, Tesla co-founder and CEO Elon Musk and JPMorgan Chase CEO Jamie Dimon — isn't subject to ethics rules. Meanwhile, whether there are links among the arms deal, the Saudi investment and the loans, future steps will seem fraught.

Schwarzman's relationship with Trump is echoed in the next generation. Jon Gray, Blackstone's global head of real estate, met with Trump when the president-elect was interviewing candidates for Treasury secretary even though he supported Hillary Clinton.

Gray, 47, and Kushner, 36, have known each other for at least four years. They both had much to celebrate in March 2013 at the anniversary party for the New York Observer, a newspaper the Kushners own. Gray was coming off a year that saw Blackstone close on $13.3 billion of capital pledges for what was then the world's biggest private-equity real-estate fund. He had been named to the Blackstone board, a sign he was being groomed for the top job at Schwarzman's company.

'25 TO WATCH'

Days earlier, the Observer named Gray among "25 to Watch" for its annual list of "100 Most Influential New Yorkers." The paper has often heaped praise on those with whom its owners might do business, and the recommendation to watch Gray was prescient. Shares in Blackstone doubled in 2013, thanks in large part to Gray's real-estate deals. These included the December 2013 initial public offering of Hilton Worldwide Holdings, which became the most profitable private-equity deal on record, and would later play a key role in Blackstone's search for investors outside the U.S., notably in China.

All of this was happening as Blackstone was quietly financing two Kushner endeavors.

In June 2013, Kushner and CIM Group, a Los Angeles-based real-estate investor, bought an office building in Manhattan's financial district. Though documents filed with New York show Deutsche Bank issued the group an $88 million loan for the property at 2 Rector St., Blackstone was also among the project's lenders, according to a person familiar with the transaction. CIM and Kushner repaid the loan in full in March 2016 with the roughly $225-million sale of the property to investors, including Cove Property Group and Bentall Kennedy.

UNDISCLOSED PARTNERS

A similar arrangement enabled Kushner Cos.' purchase of five Jehovah's Witnesses warehouse and printing buildings that October. Documents show Natixis Real Estate Capital loaned Kushner's consortium $249 million for the deal. Again, Blackstone was among the undisclosed partners.

The buildings, in the Brooklyn neighborhood known as Dumbo — the acronym for Down Under the Manhattan Bridge Overpass — were the first step in realizing Jared Kushner's dream of a new business hub for startups and technology companies. The Witnesses' headquarters, famous for its red "WATCHTOWER" sign, wouldn't come until later.

Last August, Kushner Cos. and its partners bought the building with $376 million in loans from a limited liability company controlled by Blackstone Mortgage Trust. The deal came a few weeks after Trump briefly eclipsed Clinton in the polls. Kushner, still in his role as CEO, announced plans to transform the property "into one of the marquee urban office campuses anywhere in the country, let alone New York City."

The future success of the development is far from certain, as large office tenants still haven't warmed to Brooklyn, Bloomberg reported earlier this month. Kushner Cos. will begin looking for companies to move into the Watchtower building soon.

PURCHASING POWER

Two things are more certain. First, the Saudis were very happy with the arms sale. Second, Blackstone's securing the pledge from Saudi Arabia's Public Investment Fund moves the company closer to its goal of having more than $100 billion of purchasing power for infrastructure projects, an asset type where private investment has been limited by lengthy planning and permitting processes.

Thanks to the Saudi boost, Blackstone shares are once again above their initial public offering price of $31 after slumping two years ago. That means Schwarzman, as well as having Trump's ear, has about $500 million more in net worth.

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