Jack Schlossberg's World 'Will Never Be the Same' After Sister Tatiana's Heartbreaking Death at Age 35: 'She Was My Best Friend'

Jack Schlossberg got vulnerable about what it's been like to endure "a deeply, deeply personal tragedy" while running for Congress, as his sister Tatiana Schlossberg was just 35 when she passed away from acute myeloid leukemia in December 2025.

Tatiana first received the diagnosis in May 2024 after giving birth to her second child.

"I don’t think I’ll ever process it," the 33-year-old confessed to Vanity Fair of his sibling's death. "I don’t think I’ll ever…. The world will never be the same for me, not only since she passed away, but since she was diagnosed with cancer about two years ago."

"She was my best friend," the son of Caroline Kennedy and Edwin Schlossberg gushed. "We could finish each other’s sentences. And no one loved me or was a bigger fan of me of anyone else than my sister. So I miss her all the time. Every day I think about her."

That being said, John F. Kennedy's grandson noted there's a silver lining, as her death motivated him to "do everything I can with every waking moment I have, because I realize it could have just as easily been me."

"I have an obligation to her, not just to myself, to make the most out of my precious life and all that I’ve been given in this life to give back to others and make sure that we can fund cures for the type of cancer that took her life, and for other types of cancer," he spilled.

"So it’s made me all the more motivated, engaged, and focused on making the most out of my life, and I think that there’s no higher calling than, than public service, and to me, I think politics is a noble profession, and one that I would be fantastic at serving this district as," he expressed as he runs for Manhattan’s 12th Congressional District. "So she wanted me to win, and I intend to honor her by doing just that."

Jack paid tribute to his sister via social media on January 5 — the same day her funeral was held — by sharing an old photo and quotes.

He also included Tatiana's own words, with one passage reading, "It's up to us to create a country that takes seriously its obligations to the planet, to each other, and to the people who will be born into a world that looks different than ours has for the past 10,000 years or so. Essentially, what I'm describing is hard work with possibly limited success for the rest of your life. But we have to do it, and at least we will have the satisfaction of knowing we made things better. Come on, it will be fun (?)."