Tatiana Schlossberg's cousin Maria Shriver is mourning her untimely death at the age of 35. "I return to this space today to pay tribute to my sweet, beloved Tatiana, who left this earth today. I return to this space to pay tribute and honor her loving and supportive family, who came together and did everything they possibly could do to help her," Shriver, 70, wrote via Instagram on Tuesday, December 30. "I return to this space heartbroken because Tatiana loved life. She loved her life, and she fought like hell to try to save it. I cannot make sense of this. I cannot make any sense of it at all. None. Zero." The JFK Library Foundation announced Schlossberg's death via Instagram on Tuesday. "Our beautiful Tatiana passed away this morning. She will always be in our hearts," read the statement signed by Tatiana's husband, George Moran, their two children, Edwin and Josephine, her parents, Edwin Schlossberg and Caroline Kennedy, her siblings, Jack and Rose Schlossberg, and her sister-in-law, Rory Schlossberg. Tatiana Schlossberg Family Guide: Meet Her Husband, Their 2 Kids and More In her latest social media post, Shriver praised Tatiana as a "great journalist" who used her words "to educate others about the earth and how to save it." "She created a beautiful life with her extraordinary husband George, and children Eddie and Josie," Shriver continued. "She fought like a warrior. She was valiant, strong, courageous. ... Tatiana was the light, the humor, the joy. She was smart, wicked smart, as they say, and sassy. She was fun, funny, loving, caring, a perfect daughter, sister, mother, cousin, niece, friend, all of it..." One month earlier, Tatiana - a journalist and author who was the granddaughter of late U.S. President John F. Kennedy - publicly shared her terminal cancer diagnosis. In a New Yorker essay, she revealed she'd been given a year to live after learning she had acute myeloid leukemia following the birth of her second baby. "I did not - could not - believe that they were talking about me. I had swum a mile in the pool the day before, nine months pregnant. I wasn't sick. I didn't feel sick. I was actually one of the healthiest people I knew," she wrote in November. "I had a son whom I loved more than anything and a newborn I needed to take care of." Inside Tatiana Schlossberg's Cancer Battle With Acute Myeloid Leukemia After trying multiple treatment methods, Tatiana was informed of her life expectancy in January. "My first thought was that my kids, whose faces live permanently on the inside of my eyelids, wouldn't remember me," she recounted. "My son might have a few memories, but he'll probably start confusing them with pictures he sees or stories he hears. I didn't ever really get to take care of my daughter - I couldn't change her diaper or give her a bath or feed her, all because of the risk of infection after my transplants. I was gone for almost half of her first year of life. I don't know who, really, she thinks I am, and whether she will feel or remember, when I am gone, that I am her mother." Elsewhere in her essay, Tatiana expressed her gratitude to her husband of eight years, Moran, and her family. According to Tatiana, Moran "did everything for me that he possibly could" amid her illness. "I know that not everyone can be married to a doctor, but, if you can, it's a very good idea," she noted. "He is perfect, and I feel so cheated and so sad that I don't get to keep living the wonderful life I had with this kind, funny, handsome genius I managed to find." A Comprehensive Guide to the Entire Kennedy Family: From JFK to RFK Jr. As for her family, Tatiana credited them with holding "my hand unflinchingly while I have suffered, trying not to show their pain and sadness in order to protect me from it," adding that their support "has been a great gift, even though I feel their pain every day." In her latest post, Shriver urged her followers to read Tatiana's words and savor every moment of life. "May we all hold Tatiana's family in our collective embrace not just today, but in the days ahead, and may each of you who read this know how lucky you are to be alive right now," she wrote. "Please pause and honor your life. It truly is such a gift ♥️."