Sascha and Alexander Pinczowski were world travelers who friends described as kind-hearted and quick to make those around them laugh.
The siblings, who died in the Brussels terror attacks, were Dutch nationals who lived in New York. They intended to become U.S. citizens, according to Jim Cain, the former U.S. ambassador to Denmark, whose daughter, Cameron, was dating Alexander.
Cameron and Alexander planned on getting married, Cain told NBC News, and both Alexander and his sister wanted to get American citizenship — "Alex, of course, after he married our daughter."
The brother and sister had come to Brussels via the Netherlands, where they visited family, according to CBS New York. Other news outlets, including Dutch newspaper Algemeen Dagblad, reported their father is from Maastricht, a town in the Netherlands.
They had just arrived at the Brussels airport to fly back to New York and were on the phone with a relative when two explosions went off in quick succession. A third blast later went off in a metro station.
ISIS has claimed responsibility for the attacks, which killed at least 31 and injured more than 270.
The Pinczowskis hadn't been heard from since their phone line went dead during the bombings. Cain confirmed their deaths on behalf of the family Friday.
According to friends, the family had spent some time living in Germany.
Alex Kneeshaw, who has known the Pinczowskis for more than 15 years, told the New York Daily News that Sascha was her best friend.
"We lived in Germany together, where I met the whole family and have been a part of it ever since. She is the kindest, goofiest, and (most) down-to-Earth girl I have ever met," she told the paper.
"She is the only friend that after a year or two of not seeing her we could sit down and act like no time had passed," Kneeshaw said. "When I moved back to America, Sascha came and stayed with me for two weeks to help with the move and support such a big change for me."
Another friend, Mark Lewis, told People Magazine the siblings were "very close" with each other.
"They are sweet and wonderful people," he said, adding that Alexander was an "incredibly friendly, dog-loving person" who had a lot of friends and had a passion for cooking.
Sascha graduated from Marymount Manhattan College in 2014, according to a LinkedIn page that appeared to belong to her. She had recently been a production intern for Shiraz Events, a New York events company, and had also been an event production intern at UNICEF.
The president of Shiraz Events said the company is "heartbroken" over her death.
"We remember her as a warm and lively presence during her too brief time with us," Shai Tertner told NBC New York. "Her maturity, motivation, humor and professionalism were marked characteristics in someone of her young age and we felt that she had a great future in our industry. We will miss her tremendously."
New York Gov. Andrew Cuomo called the terrorists who killed them cowards.
"On behalf of all New Yorkers, I extend our deepest prayers and condolences to the Pinczowski family, as well as all those who lost loved ones in Tuesday's heartbreaking attacks," Cuomo said in a statement Friday.
The Belgium Foreign Office had only confirmed nine of the deceased's nationalities Friday: one Peruvian, three Dutch, one from the United Kingdom, one Chinese, two Americans, and one French. Their identities had not been made public.
The family has not spoken publicly since news of Sascha and Alexander's deaths. On Thursday, after being informed that Sascha and Alexander weren't on the list of wounded victims, the family thanked the Dutch Embassy and Delta Airlines for their help.
"We especially thank all of our friends and family, across two continents, for their expressions of love, support and prayers for Sascha and Alex. We ask for continued prayers and privacy during this time of grieving as we await final closure."