Evan Vucci/AP
(CNN) —  

Fiona Hill, the top official on Russian affairs at the National Security Council, will depart the Trump administration this summer, according to two people familiar with the matter.

Hill, a former Brookings scholar and skeptic of Russian President Vladimir Putin, oversaw rocky Washington-Moscow ties over the past two and a half years. She’s expected to remain in her current post at least through Trump’s expected meeting with Putin at next week’s G20 summit in Osaka, Japan.

She’ll be replaced by Tim Morrison, an arms control specialist who currently serves as the top non-proliferation official at the NSC.

Morrison joined the administration last August and is widely considered a hardliner on nuclear policy – his area of expertise. His hawkish views seem to align with those of White House national security adviser John Bolton who has worked toward transforming the NSC into an entity that is hyper-focused on executing the President’s agenda by bringing in more political appointees and reducing the number of career officials on his staff.

An NSC spokesman declined to comment on personnel matters.

Hill’s decision to serve on Trump’s NSC was viewed as an intriguing move at the start of the administration.

A critical biographer of Putin, Hill’s views sometimes seemed at odds with Trump’s own desire to improve relations with the strongman leader who Trump, as a candidate, often spoke of admiringly.

One source close to Hill told CNN they were surprised that she seemed to develop a good relationship with Bolton after he was brought in to replace H.R. McMaster last March.

“I thought she might leave when he (Bolton) was appointed but he asked her to stay for a while. She knows Europe well and was an excellent interlocutor for European allies,” the source said.

Hill served during a contentious period for Washington and Moscow as relations soured over allegations of Russian meddling efforts in the 2016 US presidential election. Trump has viewed the investigations into those efforts as challenges to his legitimacy, and cast doubt on US intelligence findings on Russia’s role.

Over the course oSf Trump’s presidency, he has met and spoken by phone with Putin more than a dozen times – including a phone call to congratulate him on an election victory after being instructed by aides not to.

In 2018, Trump infamously sided with Putin over his own intelligence agencies on the issue of election interference after their one-on-one sit-down in Helsinki, Finland.

Despite the worsening relations – which also include disputes over Ukraine and the attempted poisoning of an alleged spy in Britain – Trump has continued to express interest in improving ties to Russia. That includes potentially negotiating a new nuclear treaty with Russia and China.

But the same source close to Hill told CNN that her departure leaves a void in an administration that already lacks expertise on European issues.

“There’s a real void now. Add to that the fact that there’s only an acting Assistant Secretary for Europe and still empty Europe slots at DoD … bottom line, the administration has very little capacity on Europe at a time when there’s considerable challenges,” the source said.