Two days after his old pal, former New York City Mayor Michael Bloomberg, roasted him at the Democratic National Convention, Donald Trump attacked him in a classic Trump manner.

"'Little' Michael Bloomberg, who never had the guts to run for president, knows nothing about me," Trump wrote on Twitter Friday morning. "His last term as mayor was a disaster!"

Trump's tweets came after a report in the New York Post that claimed his camp was blindsided by the tone of Bloomberg's endorsement of former Secretary of State Hillary Clinton.

Former New York City Mayor Rudy Giuliani, a close Trump confidant, has gone on the record saying that the campaign aggressively courted Bloomberg's endorsement.

"I didn't know until you did that Mike would give a speech at the Democratic Party convention," Giuliani told the Post Thursday.

"We heard that Mike was going the other way and that any meeting with him wouldn't be useful."

During the DNC, Bloomberg said, "Most of us don't pretend that we're smart enough to make every big decision by ourselves. And most of us who have our names on the door know that we're only as good as our word. But not Donald Trump.

"Throughout his career, Trump has left behind a well-documented record of bankruptcies, thousands of lawsuits, angry shareholders, and contractors who feel cheated, and disillusioned customers who feel ripped off. Trump says he wants to run the nation like he's run his business. God help us."

Bloomberg and Trump's words for each other are a far cry from their prior relationship. Throughout Bloomberg's time as mayor, he and Trump were cordial friends who often golfed together.

Bloomberg also made two appearances on "The Apprentice."