The Trump administration plans to accept a luxury Boeing 747-8 plane as a donation from the Qatari royal family that will be upgraded to serve as Air Force One, in possibly the biggest foreign gift ever received by the U.S. government, a senior official with direct knowledge of the matter said.

The plane will then be donated to President Donald Trump’s presidential library when he leaves office, the official said, allowing him to continue using it as a private citizen.

The plan raises substantial ethical issues, given the immense value of the lavishly appointed plane and the fact that Trump plans to use it after he leaves office. Sold new, a commercial Boeing 747-8 costs in the range of $400 million.

Trump’s own private plane, known as “Trump Force One,” is an older 757 jet that first flew in the early 1990s and was then used by Microsoft co-founder Paul Allen. Trump bought it in 2011. The Qatari jet, if Trump continued flying it after leaving office, would give him a substantially newer plane for his own use.

The plan -- reported earlier by ABC News -- is expected to be announced in the coming days, as Trump makes the first extended foreign trip of his presidency to three nations in the Middle East, including Qatar. It will fulfill the president’s desire for a new Air Force One, after repeated delays involving a government contract to Boeing for two new jets to serve that purpose.

Trump toured the Qatari-owned 747, which is just more than a decade old, while it was parked at the Palm Beach International Airport in February. The New York Times reported then that the jet was being considered as a possible new Air Force One.

The plane being donated by Qatar is expected to be retrofitted by a military contractor called L3Harris, in Texas, and that work can begin once the government approves how the plane is being acquired, the official said. It is expected to be finished being equipped with military capabilities by the end of the year, the official said, allowing Trump to use it while in office.

A White House spokesperson did not respond to a request for comment. A Defense Department official said Sunday that the Air Force has not yet reached any agreement on a contract to refurbish the Qatari 747 to make the security upgrades and modifications necessary for an Air Force One, and the Air Force could not legally do so until it actually took ownership of the plane.

Assuming that were to happen, the official said, it would still take an extended period of time to complete the contract and, more important, to do the actual upgrades and modifications.

“We’re talking years, not months,” the Defense Department official said, speaking on condition of anonymity to discuss sensitive details about a future Air Force One.

The model that the government is using for addressing some of the ethical issues raised by the donation, the official said, is the one followed by President Ronald Reagan’s presidential library when it received the Air Force One he had flown on after it was retired from use. But at the time, Reagan did not use the plane to fly around himself. It was set up in the museum portion of his library.

Another person with knowledge of the effort to acquire the plane said that the Qataris had initially offered to donate it immediately to the Trump library, and then have Trump use it while in office. But government lawyers said that would be a violation of the emoluments clause of the Constitution, the person said.

The current plan has been signed off on by government lawyers who concluded it does not violate the emoluments clause of the Constitution and that the Defense Department can accept the gift, the official said.

This article originally appeared in The New York Times.