Marjory Stoneman Douglas High School student Emma Gonzalez, centre right, embraces Jennifer Hudson near the conclusion of March for Our Lives in Washington, D.C. Picture: Matt McClain/AP

Jennifer Hudson wasn't just one of several celebrity performers during Saturday's March for Our Lives rally in Washington. She is also the daughter, sister and aunt of victims of gun violence.

After her stirring performance before hundreds of thousands of demonstrators rallying for action against gun violence, the Oscar-winning singer spoke out about the march and her personal tragedy.

"It is almost impossible to understand what the victims, the families, are going through, what they feel, or even to be able to relate to a situation like this unless you've been in it," Hudson told CNN's Van Jones. "So for people who are watching ... know that it can be anybody. It can happen to anybody."

She added: "To me, the saddest thing is no one ever reacts until it happens to them, and then it's too late."

Three close members of Hudson's family were fatally shot in October 2008: mother Darnell Donerson, 57, brother Jason Hudson, 29, and nephew Julian King, 7. A jury found William Balfour guilty of the murders, and a judge sentenced him to three consecutive life terms.

Prosecutors said Balfour - who at the time was married to but separated from Hudson's sister, Julia - had been jealous and angry over his failing marriage.

Video by: Monica Akhtar/The Washington Post

The bodies of Jason Hudson and Donerson were discovered inside the matriarch's Chicago home. Julian, who was Julia Hudson's son, was initially reported missing, prompting a frantic search for the boy.

"My greatest fear has already happened, my greatest hope is for having my child. I just want my son," Julia Hudson said at the time. "That's all I have to say. Just let my baby go."

His body was discovered three days later inside a parked car.

In the immediate aftermath of the crime, Jennifer Hudson and her family announced that they had started a foundation in honor of their slain relatives.

"The specific purpose of the foundation is to care for the needs of families who have lost relatives to a violent crime," the family said in a statement. "This encompasses their basic needs of food, clothing and shelter as well as grief counseling."

Jennifer Hudson and her sister started Hatch Day in honor of Julian King; their foundation collects and distributes Christmas presents to children on the boy's birthday.

On Saturday, the singer closed out the march in D.C. with a rendition of "The Times They Are A Changin.'"

Later, Hudson said, "A day like this is almost like reliving it, over and over again."

"It's obviously something extremely close to home for that reason, because you instantly connect," she continued. "There's very few people who know what a moment like this means, what it represents, everything that it entails. I can't help but to be affected or taken by it."

Since 2008, Hudson has spoken publicly about the killings of her relatives only a handful of times, but the mass shooting in Parkland, Florida, last month touched a deep nerve for her. Every time she sees one particular clip - of a grieving Lori Alhadeff, whose daughter was killed in the Parkland shooting - Hudson sobs, she said.

"I just spent the last two hours putting the burial arrangements for my daughter's funeral, who is 14!" Alhadeff yells into the camera. "President Trump, please do something! Do something, action! We need it now! These kids need safety, now!"

"She was just screaming out," Hudson said. "I understood every inch of her frustration ... She's angry, for one, because this is nonsense. Then, two, no one understands."

Hudson continued: "She's pouring out. I could hear it. I knew where it came from ... It's like reliving it. And I was like, unfortunately, 'Welcome to my club.' My heart completely went out to her. I was like, you're not alone. I understand everything you're feeling."