U.S. President Donald Trump has granted a full pardon to former media mogul Conrad Black, with the White House calling him "entirely deserving" of the gesture.

Black, who once described Trump as an “old friend” and recently published a glowing biography of the president, served nearly 42 months in a Florida prison after he was convicted for fraud and obstruction of justice in 2007. He was also fined US$125,000.

Black said Trump called him last week to personally deliver the news.

In an interview with CTV News’ Omar Sachedina Wednesday night, Black said he initially thought the phone call was a prank, but quickly realized that it really was the president of the United States on the other line.

Black said “it was very, very gratifying” to receive the pardon.

“It has not been a day at the beach to go through all this,” he said. “I was innocent … There was no substance to any of the charges. There never was. The whole thing gradually disintegrated.”

Black also issued an exhaustive 1,698-word statement expressing his gratitude to Trump and others who lobbied on his behalf over the years.

“He could not have been more gracious and quickly got to his point, that he was granting me a full pardon, that would ‘Expunge the bad wrap [sic] you got,’” Black wrote.

“The American criminal justice system is frequently and largely evil; I was convicted for attempted obstruction of injustice. It was never anything but a smear job.”

In a statement, White House press secretary Sarah Sanders described Black as “an entrepreneur and scholar” who has a “distinguished reputation for helping others” and worked as a tutor in prison.

“In light of these facts, Mr. Black is entirely deserving of this Grant of Executive Clemency,” the statement read.

Black has long been a vocal supporter of Trump. Last year, Black published a flattering biography of Trump, "Donald J. Trump: A President Like No Other,” in which he highlighted what he considers the president’s biggest successes.

After the book was published, political observers speculated that Black may have been angling for a presidential pardon. He denied doing so Wednesday in the interview with CTV News, but offered the hypothetical scenario that if he was a Trump critic, the president may have acted differently.

“I wouldn’t count on him responding as he has. But that is entirely hypothetical,” he said. “There is no doubt in my mind that while he was happy to do it for personal reasons, he is satisfied, and the White House counsel confirmed him in this, that I never should have been charged and certainly never should have been convicted.”

Black doesn’t think his book had anything to do with Trump’s decision to issue the pardon.

“I have no reason to believe he’s read it and he’s never mentioned it to me,” Black said Wednesday. “I take him at his word that his motive was what he said it was.”

Black said that he and Trump are “not close now,” but were always friendly in the past, adding that they were business associates on a project in Chicago and were neighbours in New York and Palm Beach.

“I have not heard from him since he was president-elect, up until last week, when he called,” he told Sachedina.

Black said he does not have a direct line to the U.S. president.

“I would never dream of bothering a person in a position like that. I would never have occasion to presume to phone the President of the United States,” he said. “He’s got other things to do than take calls from me.”

In 2015, when Trump was running to be the Republican nominee for president, Black wrote a piece for The National Review calling Trump “the good guy” in the race.

The article caught the attention of then-candidate Trump.

"What an honor to read your piece," Trump tweeted. "As one of the truly great intellects & my friend, I won't forget!!"

Black responded in kind.

"Many thanks, Donald and all good wishes in helping to clean up the American government. Honored to be your friend," he tweeted.

His feelings on the Trump presidency haven’t changed. While he conceded that Trump has “stylistic foibles,” Black isn’t bothered: “He is who he is and I think he’s done an excellent job.”

Black previously headed Hollinger international, a global newspaper publisher that published The National Post, The Daily Telegraph and The Jerusalem Post. He famously renounced his citizenship to Canada in 2001 to become the Lord Black of Crossharbour, his official title as a British lord.

In 2007, Black was convicted of three counts of fraud and one of obstruction of justice in a Chicago court and sentenced to six and a half years in jail. Two of the criminal fraud charges were dropped on appeal. But a conviction for felony fraud and obstruction of justice were upheld in 2010.

He has been banned by the Ontario Securities Commission from acting as a corporate director or officer of a public company in Ontario. He was also removed from the Order of Canada.

With files from The Canadian Press