Joe Biden has expressed regret about deciding not to run for president and insisted he would have been able to beat Donald Trump if he had been the Democratic candidate.

The former Vice President to Barack Obama ruled out running for office in 2016 in a race that would have seen him pitted against Hillary Clinton and Bernie Sanders. This was partly prompted by his son’s brain cancer diagnosis and subsequent death.

“I had planned on running for president and although it would have been a very difficult primary, I think I could have won,” Biden said at a speech at Colgate University in Hamilton, New York, late on Friday night.

“I don’t know, maybe not. But I thought I could have won. I had a lot of data and I was fairly confident that if I were the Democratic Party’s nominee, I had a better than even chance of being president.”

But Biden said he did not regret the time he was able to spend with his son before he died.

“But do I regret not being president? Yes,” he said. “I was the best qualified.”

The politician said his son’s illness made him feel unable to run. Talking emotionally about his son’s death, he said he had “lost part of my soul” when he passed away.

“No one should ever seek the presidency unless they are able to devote their whole heart and soul and passion into just doing that,” Biden told ABC News last year. “Beau was my soul. I just wasn’t ready to be able to do that. My one regret is my Beau’s not here. I don’t have any other regrets.”

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After his older son, who was a war veteran, died in May of 2015, he released a statement, saying: "Beau Biden was, quite simply, the finest man any of us have ever known”.

Beau’s death is not the only tragedy to have hit the family. Beau was just two when his mother, Biden’s wife Neilia Hunter, was killed in a car crash in 1972, which also took the life of the former Vice President’s one-year-old daughter.

Last December, Biden, who has been jointly elected twice as the running mate of former President Obama, said he intended to run for president in 2020.

Asked if he would run for office, he said: “Yeah, I am. I am going to run in 2020.”

When asked which position he would run for, he replied: “For president. And also, you know so, what the hell man, anyway.”

Probed out whether he was joking, Biden said: “I’m not committing not to run. I’m not committed to anything. I learned a long time ago, fate has a strange way of intervening.”