Donald Trump Jr. is being paid $100,000 to participate in a Texas public university speaking series sponsored by the company of a major Republican donor - a fee that is as much as double what President Donald Trump's eldest son appeared to have sought on the lecture circuit before this year.

In July, Trump Jr. signed a contract with the University of North Texas agreeing to give a half-hour speech and participate in a 30-minute question-and-answer session in October in exchange for a $100,000 stipend, according to documents first obtained by the North Texas Daily, the student newspaper. The university provided a copy of the contract to The Washington Post.

Trump Jr. was invited by organizers of the UNT Kuehne Speaker Series, whose top sponsor this year is a corporate tax services firm headed by G. Brint Ryan, a UNT alum and well-connected GOP donor in Dallas who advised President Trump on tax policy during the campaign.

In an interview, Ryan said that the series is paid for by private donations, not public funds, adding that Trump Jr.'s appearance will help raise money for National Merit Scholarships for UNT students.

"I don't think we've paid that much before," Ryan said of Trump Jr.'s stipend. But he said he did not have any qualms about the amount, noting that the series hopes to draw as many as 2,000 paying guests to hear the president's son on Oct. 24 at the AT&T Stadium in Arlington, Texas - the home of the Dallas Cowboys.

"The fee is not important - what's important is the net result," he said. "This is not a deal to sponsor Donald Trump Jr. This is an effort to raise as much money as possible for scholarships."

"If Chelsea Clinton wants to come next time, that's great," Ryan added.

Tickets for the speaking series are only available through table sponsorship, ranging from $5,000 to $100,000, according to the event's website. As a presenting sponsor, Ryan's tax services company, Ryan LLC, paid at least $100,000 to support the series.

Kelley Reese, a spokeswoman for UNT, said the speaking series has raised $1.65 million for scholarships since it began in 2013, with the first awards expected to go out this year to five students.

The goal of the series is to present "timely and stimulating perspectives on our world as it pertains to national security, our economy, and topics that are of interest to the university's many and varied communities," she said in a statement.

Trump Jr. did not respond to requests for comment. A spokeswoman said that the 39-year-old is "a popular public speaker who has been participating in speaking engagements domestically and internationally for over a decade. Additionally, this particular speech has been in the works for many months."

Earlier this year, he served as the commencement speaker for American University in Dubai for an undisclosed sum.

The fee for Trump Jr.'s UNT speech appears to be twice as much as he charged to give paid speeches before his father ascended to the Oval Office, according to his past speaker bureau listings.

In early January 2017, the website of one booking agency, BigSpeak, listed his fee as more than $40,000 per appearance, according to a Huffington Post report. A listing on the website of another agency, All American Speakers, that does not appear to have been updated since the election says that the fee to hire Trump Jr. to speak begins at $50,001.

During last year's presidential campaign, Trump Jr. tweeted critically about paid speeches given by former President Bill Clinton while his wife Hillary Clinton was Secretary of State, in one case describing a six-figure fee Clinton received as "#paytoplay."

The invitation to Trump Jr. from UNT, a large public research university north of Dallas that serves a student body nearly 38,000, has drawn criticism from students and alumni. In an editorial last month, the student newspaper noted that Trump Jr. is under federal scrutiny for meeting during the campaign with a Russian lawyer with Kremlin connections. The editorial called the invitation "a tone deaf and utterly irresponsible decision."

Reese told The Washington Post that "as a public university that supports the expression of differing points of view as part of the learning process, UNT welcomes speakers who represent all viewpoints, including conservative, liberal and progressive political ideology as well as all positions in between."

Ryan also defended the invitation, saying Trump Jr. will be a big draw.

"We have gotten a lot of feedback on social media, but my view is we are trying to find speakers that are relevant, that are timely, that are in the middle of important current events," he said.

"He's in the middle in a lot of stuff, whether you love him or hate him," Ryan added. "People are going to come out and hear him speak."

Ryan said he first broached the idea to Trump Jr. when they had dinner together several months ago, and later the Kuehne Speaker Series committee extended the invitation to the president's son.

Named after UNT alum and Texas oil executive Ernie Kuehne, the series' past speakers include former New York Mayor Rudolph Giuliani, former CIA director Michael Hayden and Fox Business correspondent Charles Gasparino.

Ryan, whose firm's clients include American Airlines, Chevron and Walmart, is a prominent figure in Texas GOP circles, donating large sums to boost then-Gov. Rick Perry, who is now U.S. Energy Secretary, and Sen. Ted Cruz, federal filings show. He contributed more than $83,000 to the Republican National Committee last fall, according to Federal Election Commission data.

In the general election, he briefly served as an informal adviser to Trump, meeting with the candidate to share advice about tax policy, Politico reported in October.

Ryan said that while he has offered comment on "certain aspects of tax reform" to Trump, he is not currently advising the administration. And he rejected the notion that inviting Trump Jr. to UNT could be a way to gain favor with the president.

"I don't really need any access," he said.

The Kuehne Speaker Series website describes Trump Jr. as "a businessman, and the oldest son of the 45th President of the United States, Donald Trump."

Under his contract, Trump Jr.'s fee is non-refundable unless he cancels on the university, the document shows. UNT agreed to pay for first-class air travel and hotel accommodations, with expenses not to exceed $5,000.

In return, Trump committed to attend a two-hour dinner with eight guests the night before the speech, along with a VIP breakfast and reception the following day. The university agreed to provide him the questions that will be posed in the question-and-answer session ahead of time.

Alice Crites contributed to this report.