(CNN) It would have hardly seemed likely back in April that a little-known Ukrainian gas company would be propelled to the center of a massive US political scandal.

But these are not ordinary times.

On April 21, US President Donald Trump spoke by phone with Ukrainian president-elect Volodymyr Zelensky, who had just won a resounding victory at the polls. Kurt Volker, the US Special Representative for Ukraine negotiations, described it as a routine congratulatory call.

But within days of Zelensky's win, the New York Times published a story that resurfaced questions about Democratic presidential contender Joe Biden and his son, Hunter Biden, in Ukraine. At the center of the story -- pushed in good part by Rudy Giuliani , Trump's lawyer and political attack dog -- was the role of Hunter Biden on the board of Burisma, a natural gas company.

The Bidens and Burisma were the focus of a July 25 call between Trump and Zelensky, a conversation that spurred a whistleblower complaint.

"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that so whatever you can do with the Attorney General would be great," Trump said, according to notes prepared by staff in the White House situation room.

Trump was referring to investigations into Burisma, following on the insinuation -- an unproven one -- that Joe Biden tried to have Ukraine's top prosecutor ousted in 2016 to stop investigations of Burisma, to benefit his son.

That version of events has not held up: Burisma had indeed been investigated, but at least one former official in the Ukraine prosecutor's office said the investigation into Burisma had already been shelved by the time Joe Biden lobbied for the replacement of Ukraine's prosecutor.

Still, in the July 25 call, Zelensky appeared to promise to have a new prosecutor look into the case. "Since we have won the absolute majority in our Parliament, the next prosecutor general will be 100% my person, my candidate, who will be approved by the parliament and will start as a new prosecutor in September," he said, according to the transcript.

Whether the Ukrainian government will deliver what Trump wants -- an investigation of the Bidens -- remains to be seen.

A prominent Ukrainian lawmaker told CNN Thursday that a new investigation of a Ukrainian firm at the heart of a growing US political scandal would not involve Joe or Hunter Biden.

Valentyn Nalyvaichenko, a leading parliamentarian and a former head of Ukraine's domestic intelligence agency, told CNN prosecutors were looking to open an investigation into Burisma. Nalyvaichenko added, however, that the role of Hunter Biden would not be examined, as far as he was aware, and that Joe Biden's efforts during his tenure as vice president to dismiss a former Ukrainian prosecutor general will not form part of the restarted investigation.

"This investigation is about Ukraine's corruption at the top," Nalyvaichenko said. "It is about getting to the truth for Ukrainians."

The Ukrainian Prosecutor General's office has not said whether a probe of Burisma had been reopened, and declined comment to CNN. Previous probes into Burisma by Ukrainian prosecutors over the years have been dropped or gone dormant. Hunter Biden no longer works for Burisma.

The Ukrainian government, it appears, will be walking a fine line in reopening a probe of Burisma.