SEAN and Kim Copeland had taken their family from the Texas Hill Country to Europe for a summer vacation -- seeing the Running of the Bulls in Pamplona in Spain and exploring the sights in Barcelona. Then, they traveled to the French Riviera for Bastille Day.

It was there, in Nice, that a Tunisian-born émigré drove a truck into a crowd celebrating the French National Day on Thursday night, killing at least 84 people and wounding many others in an apparent terrorist attack.

Sean Copeland, 51, and his 11-year-old son, Brodie, were among them.

"We are heartbroken and in shock over the loss of Brodie Copeland, an amazing son and brother who lit up our lives, and Sean Copeland, a wonderful husband and father," Jess Davis, a family friend who is speaking for the Copelands, said in a statement to The Washington Post. "They are so loved."

The University of California also said Friday that three study-abroad students were injured in the Nice attack and another student was "still unaccounted for."

Davis said Sean Copeland's wife, Kim, and his older children, 29-year-old Maegan and 22-year-old Austin, survived the attack. Two of Sean Copeland's brothers are set to fly to Nice with State Department officials, Davis said, and will travel back to the U.S. with Kim, Maegan and Austin Copeland.

At the White House, President Barack Obama spoke Friday about the father and son from Texas.

"Their family, like so many others, are devastated," Obama said in the East Room. "They're grieving. They need all the love and support of our American family as they grapple with an unimaginable loss and try to get through what are going to be very difficult days."

Texas Gov. Greg Abbott said Friday that the French flag was being flown over the governor's mansion in remembrance of the victims in Nice, including the Copelands.

"While every heinous attack like this is tragic, this latest one hits close to home," Abbott said in a statement. "Cecilia and I ask that Texans join us in praying for all of the victims, and especially the Copeland family as they mourn the loss of a devoted father and loving son."

In a statement, Sen. Ted Cruz, R-Texas, said, "We are lifting the Copeland family up in prayer, along with all of the victims who are suffering because of this heinous act of terror."

The State Department confirmed that two U.S. citizens were killed in the attack in southeastern France but did not release the victims' names.

[PHOTOS]: Truck strikes crowd in Nice, France during Bastille Day

"We express our sincere condolences to the family and friends of those killed," spokesman John Kirby said in a statement. Kirby said the State Department is "providing all possible consular assistance."

The University of California identified its missing student as 20-year-old junior Nicolas Leslie, an American who was studying at the European Innovation Academy.

His father told the Wall Street Journal on Friday that Leslie, from Del Mar, California., was with friends who jumped out of the way during the attack.

"We think he escaped the truck, but he could have been trampled," Conrad Leslie, a 55-year-old engineering consultant, told the newspaper.

A woman who answered a phone at the family's home in Southern California said the Leslies had not heard anything from authorities in France by early Friday afternoon.

"We've been contacting all the entities there," the woman, who declined to give her name, told The Washington Post. She described Nicolas Leslie as "just a very nice human being," adding: "He just got lost while he was running away."

Leslie was part of a study-abroad program at the European Innovation Academy, a nonprofit that helps students incubate ideas. He had also studied with the program in Italy.

In recent days, he was videoblogging about his experience at the academy, where his team was developing software that would allow soccer coaches to monitor how tired players are in real time.

"I really believe in this idea - and I think that if we can pull off this software, there's a very good chance that we'll have great success," he said.

After the massacre, relatives of the Copelands began expressing their heartbreak on social media .

Heather Copeland, Sean Copeland's niece, pleaded for prayers for her family.

"I don't even know how to put this in words," she posted late Thursday night. "Today was a very tragic day for my family. My uncle Sean and my cousin Brodie Copeland were killed today in a terrorist attack in Nice France while they were on vacation. A huge box truck ran over and killed 80 plus people and injured over 100.

"Please keep my family and all the other family's affected by the tragic event that occurred tonight in your prayers."

On Friday morning, she wrote: "I just want my cousin and uncle back."

Haley Copeland wrote that the Copelands - from Lakeway, near Austin - were on vacation in Europe, celebrating a birthday. Davis, the family spokeswoman, told The Post that Sean Copeland's son, Austin, turned 22 this month. Kim Copeland turns 40 on Monday, Davis said.

She declined further comment out of respect for the family.

"This is an extremely difficult time for my family and anyone who knows Sean and Brodie Copeland," Haley Copeland wrote. "Losing a loved one is hard no matter the circumstances but losing a loved one in such a tragic and unexpected way is unbearable. Prayers are much appreciated."

Sean Copeland worked as vice president of North and South America for Lexmark's enterprise software division, the company said.

"Today, Lexmark is saddened to learn that our employee and friend, Sean Copeland, and his son, Brodie, were killed in the attack in Nice, France last night," company spokesman Jerry Grasso said in a statement. "Sean was not only a terrific leader in the company but a phenomenal person who will be dearly missed.

"Our hearts go out to Sean and his family, and for everyone who is suffering in France and elsewhere from this senseless violent act."

Brodie Copeland was a fifth-grader at Lakeway Elementary. He wanted to be an actor or a comedian when he grew up, family friends said. And he was an avid baseball fan.

His mother, Kim, posted a black-and-white photo on Facebook in March, portraying a pensive Brodie standing tall on a pitcher's mound.

On Thursday, the Hill Country Baseball Club in Austin shared a photo on Facebook showing the boy on a beach, saying "our very own Brodie Copeland, as well as his father Sean Copeland, were killed during the terrorist attack in Nice, France."

The group said the photo of Brodie had been sent to them from the French Riviera.

"Nobody deserves this type of fate, especially not such a wonderful family," the post read. "You are in our hearts, thoughts, and prayers. Rest in peace, Brodie and Sean, you will be remembered by many."

"Two of the greatest men," commenter Bill Bishop wrote on the post. "We will miss you #8. You will be missed but we know you were needed for bigger and better things."

"It is hard to understand the loss but I am sure you two great men have been called and needed in a better place," he added. "You will be greatly missed but thanks for changing our lives while you were here. Stay strong Kim we are praying for you and we will see you soon."

Aaron Cable with Hill Country Baseball Club said he has worked closely with Brodie over the years and said he was "an overall talented, Renaissance-man kind of kid."

"Brodie is just a one-of-a-kind kid," Cable said, according to a statement provided by Davis, the family spokeswoman. "He's popular, he's funny, he's mature, he's fun to be around. You could have adult conversations with him when he was 9 years old."

Cable also said Sean Copeland was "one of the greatest dads you could ask for."

"He would do whatever he needed to do to make sure Brodie got baseball lessons, acting lessons, and everything he ever needed or wanted," he said, adding: "He was a good guy, who cared about his kids."

The Pastime Training Center in Frisco, Tex., posted a photo of Brodie collecting a baseball trophy.

"One of our original PTC Aces players, Brodie Copeland, lost his life today along with his father Sean, in the attacks in Nice, France," it read. "Please keep their family in your prayers."

A GoFundMe page set up for Sean and Brodie Copeland has raised more than $19,000.

"The Lakeway community is like family, and we have lost two of our members," the city's mayor, Joe Bain, said in a statement, adding: "Our thoughts and prayers are with the Copeland family in their time of mourning."

Rep. Roger Williams, R-Texas, who represents Lakeway, said on Twitter that the "loss of Sean & Brodie Copeland hits us in our core and breaks our hearts."

Rep. Lloyd Doggett, D-Texas, said Friday that he had talked to Sean Copeland's other son, Austin, a Texas State University student, to offer his support.

"Words are truly inadequate to express the depth of this loss," Doggett wrote on Twitter. "And we renew our resolve to obtain all relevant facts to determine the most effective ways to firmly combat this evil."

Rep. Michael McCaul, R-Texas, who chairs the House Homeland Security panel, said Friday morning he was saddened over a "truly heartbreaking loss of life in #Nice."

The Texas school district that includes Lakeway Elementary expressed "heartfelt condolences" in a statement.

Kirby, the State Department spokesman, said the U.S. Embassy in Paris "is making every effort to account for the welfare of U.S. citizens in Nice. Any U.S. citizens in Nice should contact friends and family directly to inform them of their well-being."

The agency said Friday morning it was still "working with local authorities to determine if other U.S. citizens were injured in the event."

Seventeen students from the Georgia Tech were reported to be in Nice celebrating Bastille Day when the driver, identified as 31-year-old Mohamed Lahouaiej Bouhlel, plowed through the crowd.

One of them, James Walker, told reporters he and his friends were facing the water after the fireworks show finished when suddenly the white truck zoomed past them from behind, narrowly missing them.

"The mirror of the truck came up and hit me on the head," Walker, an economics student who is studying abroad, told NBC affiliate WXIA. "I mean, I'm not hurt at all, but that's pretty much how close I was to it."

Brendan Phillips, another Georgia Tech student who was with Walker, described his fears of a stampede as the crowd ran toward them.

"The entire crowd of people was running toward us," said Phillips, who is also studying abroad. "So my first thought was we're going to get stampeded by people. But we turned around, ran in the same direction."

Georgia Tech spokesman Lance Wallace said in a statement Friday that the university has contacted all of its students studying in Nice and that they are "safe and accounted for."