Joe Kennedy On The Time He Got Schooled By Elizabeth Warren Kennedy spoke to ABC News' Jon Karl.

 -- “Mr. Kennedy, what is the definition of assumpsit?”

It was the first question Joe Kennedy's professor posed to him on his first day at Harvard Law School. He didn’t know the answer.

The professor was Elizabeth Warren. And Kennedy learned an important lesson that day: “Never show up for her class unprepared.”

“She was the toughest teacher on campus but the waitlist to be in her class was always a mile long,” Kennedy, now a member of the U.S. House, said of Warren, now a U.S. Senator, in an introduction speech at the Democratic National Convention Monday night. In addressing the convention, Kennedy continued an almost unbroken 60-year-long line of Kennedy representation at the Democratic conventions.

Though Kennedy relived his embarrassing first encounter with Warren on national television Monday night, he confessed to ABC News’ Jonathan Karl in an interview on “Powerhouse Politics” that what happened in real life was actually far worse.

“I had enough decency not to relive total public humiliation to the degree to what happened in front of 15 million people on national television so I took a little mercy on myself,” Kennedy joked to Karl.

“No hi, no good morning, just boom,” Kennedy recalled of the moment when Warren made an example of him in her classroom.

The moment was particularly stinging to Kennedy, who said he was still thinking of the advice his father -- Joseph Kennedy II, the eldest son of the late Bobby Kennedy -- had given him the night before. “Everybody’s going to think you’re smart, don’t open up your mouth and disappoint them,” Kennedy said his father advised.

But Kennedy’s experience in Warren’s class wasn’t all bad from there on out.

“Luckily for me there was a cute girl in the second to last row, who I still convinced to marry me after that,” Kennedy joked.

And that “cute girl” who would go onto to become his wife also became a helpful study partner, advising him later to look up another word they had come across in studying for which he didn’t know the meaning.

Sure enough, Kennedy got his second chance.

When Warren came to him for the definition of that word after passing up several students who came up empty, he was prepared this time. He recited the definition, which had written down. And for that, he recalled, the class gave him a standing ovation.

He would go on to take a second class at Harvard taught by Warren – bankruptcy law – he said, “just because she was the teacher.”

“I remember going to her office hours one time and she was hanging up on Harry Reid as they were going through the oversight of TARP, Troubled Asset Relief Program, so that she could answer questions that I had about the intricacies of bankruptcy law, which I thought was a pretty cool thing and a pretty amazing testament to her,” he recounted.

And when he graduated, it was Warren who handed Kennedy his diploma. But not before quizzing him one last time.

“As she was handing me the diploma, she asked me again, like you’re not going to get it until you know it,” Kennedy said.

On the topic of the presidential election, Kennedy was deeply critical of Republican nominee Donald Trump for seeming to encourage Russia to find emails from Clinton’s private server –- a comment Trump has since tried to downplay as “sarcasm.”

“The idea that the leader of the free world and the chief executive of the United States would in any way indicate that it was in any way okay for a foreign power to engage in espionage on a US agency regardless of what it is non-profit, political, or otherwise is outrageous,” Kennedy said.

“If Russia did in fact do that,” he continued, “that is a foreign government meddling in our electoral process and that deserves a strong, concerted response from the US government.”

He expressed confidence that Clinton will win in November but cautioned that presidential elections are always close.

“This isn’t reality TV anymore, this is real, it has real consequences,” Kennedy said.