Donald Trump’s son-in-law Jared Kushner has been named as a senior advisor to the U.S. president-elect, after playing an increasingly prominent role in preparations for Trump’s administration.

New Yorker Kushner, an Orthodox Jew, married Ivanka, one of Trump’s children, and the pair are known to exert influence over the Republican mogul and his top team, with Kushner having met British Foreign Secretary Boris Johnson this month.

Kushner, 35, earned Trump’s respect after rebuilding his father’s once-golden real estate portfolio, and led successful elements of his father-in-law’s presidential campaign, including his use of social media, for which he is now known.

Observers say his appointment this week may fall foul of U.S. anti-nepotism laws, instigated after President Kennedy appointed his brother Bobby as Attorney-General.

Critics say both Kushner and Trump have conflicts of interest, owing to their stakes in businesses whose fortunes follow policy decisions. Kushner also owns the New York Observer. It is not yet clear what, if any, divestments will be made as a result of his appointment.

In November, Trump said Kushner could “do peace in the Middle East,” suggesting he says his son-in-law as capable of mediating in peace negotiations.