It was love at first sight for Joe Biden. The University of Delaware junior had taken a spring break trip to the Bahamas and sneaked into an exclusive beach resort, where he came upon Syracuse University senior Neilia Hunter sunbathing by a pool.

"When she turned toward me, I could see she had a beautiful smile and gorgeous green eyes," he wrote in his memoir Promises to Keep. "She was lit by the unforgiving journey of a full afternoon sun, and I couldn't see a single flaw."

Joe found Neilia to be warm, bright and refreshingly down to earth, unbothered by his modest upbringing in Scranton, Pennsylvania, and Wilmington, Delaware. And as their relationship progressed, her well-to-do parents overcame any misgivings about his politics (he's a Democrat, they were Republican) and religious faith (he's Catholic, they were Presbyterian).

As such, the August 1966 wedding between Joe and Neilia appeared to be just an early milestone in their storybook romance, no one knowing their union would end in tragedy less than six-and-a-half years later.

Neilia served a crucial role in Joe's 1972 Senate campaign

As their shared journey took them to Syracuse and then to Wilmington, the couple mapped out the goals that included Joe becoming a trial lawyer and then running for public office. "We agreed on almost everything," he wrote, save for Neilia's hope that her husband set his sights on the U.S. Supreme Court.

Neilia held down the fort as their life accelerated, giving birth to Joseph "Beau" Biden III in February 1969, Robert "Hunter" Biden in February 1970 and Naomi "Amy" Biden in November 1971. Meanwhile, Joe's first attempt at politics proved successful with his election to the New Castle County Council in 1970.

Two years later, Neilia assumed a leading role in Joe's campaign against Republican J. Caleb Boggs for the U.S. Senate, serving as what her husband called the "brains" of the operation. When the Election Day dust cleared, the not-yet-30-year-old challenger had become the second-youngest person ever elected to the Senate, leaving the Bidens to wonder what could possibly come next in their rapid rise in politics.

Joe Biden and first wife Neilia, with sons Hunter and Beau, cut his 30th birthday cake at a party in Wilmington, Delaware on November 20, 1972

Joe Biden and first wife Neilia, with sons Beau and Hunter, cut his 30th birthday cake at a party in Wilmington, Delaware on November 20, 1972

The Biden's car was hit by a truck the week before Christmas

The answer came on December 18, a Monday that began with Joe heading to his temporary office in Washington, D.C., while Neilia remained at their new home in northeastern Delaware with the intention of tackling some Christmas shopping.

At approximately 2:30 p.m., Neilia was driving westbound on rural Valley Road in Hockessin, the three children accompanying her in the family station wagon. She pulled the car past a stop sign and directly into the path of a tractor-trailer, headed full-steam along Route 7 to Pennsylvania.

According to reports, the impact sent the station wagon hurling some 150 feet into an embankment, leaving "Biden for Senator" campaign literature scattered in its wake.

The family was pulled from the wreckage of the car and rushed to Wilmington General Hospital, but it was too late for Neilia and 13-month-old Amy, who were pronounced dead on arrival. The two boys were luckier, though Beau sustained a broken leg and Hunter, a fractured skull.

Joe immediately knew something terrible happened

As Joe recalled in Promises to Keep, he knew something terrible had happened after watching his sister answer the phone at his office that afternoon, a tangible feeling of Neilia's loss heightening when Valerie suggested they return home because of a "slight accident."

"She's dead, isn't she?" he responded.

A rushed flight back to Wilmington confirmed the worst of his suspicions, but Joe didn't have the opportunity to fully process his grief with his young sons still in uncertain condition. At that point, he wrote, he understood how suicide seemed a tempting option, though he knew he could never abandon Beau and Hunter with their mother and sister also gone.

Joe took little solace in the investigation that cleared the truck driver of responsibility for the crash (it was later revealed that Neilia had "either accelerated or drifted through the intersection," possibly distracted by the children in the back seat). And while he was heartened by the boys' improving conditions, the widower found himself consumed by anger, at times roaming the streets at night with the hope that someone would pick a fight with him.

Joe Biden takes the oath of office from U.S. Senate secretary Frank Valeo with his father-in-law, Robert Hunter, and son Beau at his side, in Beau's hospital room

Joe Biden takes the oath of office from U.S. Senate secretary Frank Valeo in Beau's hospital room. Joe's father-in-law, Robert Hunter, at his side.

He recovered by focusing on the well-being of his surviving sons

Joe ultimately climbed back with help from his Senate colleagues and support of his sister, though it was his focus on the well-being of Beau and Hunter that enabled all three of them to move on with their lives.

It helped that another woman came into his life when his brother set him up with fellow University of Delaware student Jill Jacobs in 1975. And when it became clear that Jill was an indispensable part of their tight-knit clan, it was the boys who pushed their old man to pop the question once again.

Shortly before their 1977 wedding, Joe asked his fiancée how she could commit herself to marriage knowing his feelings for his first wife. "Anybody who can love that deeply once can do it again," she replied.

"That's when I realized exactly what Jill's love had done for me," Joe wrote, "it had given me permission to be me again."