New York-Based Siblings killed in Brussels were 'sweet and wonderful'

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."

See photos of the siblings:

The brother and sister had come to Brussels via the Netherlands, where they had been visiting 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.

Related: New York-Based Sascha, Alexander Pinczowski Killed in Brussels Blasts

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.

Tributes and memorials around the world after the Brussels attacks:

The Pinczowskis hadn't been heard from since their phone line went dead during the bombings. Cain said an "identity match" had been confirmed for them.

Related: John Kerry: We're Determined to Thwart Foreign Fighters

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 theNew 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 aLinkedIn 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 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."

More from NBC News:
'I Was There to Help': Stories of Heroism After Brussels Attacks
Seven Detained in Raids Linked to Brussels Attacks
Why Belgium Is a 'Safe Haven' for ISIS