The actress paid tribute to her late sibling with a sweet throwback photo from their childhood.
"Happy Birthday little brother. I miss you everyday. I’ll love you forever ❤️" she captioned an Instagram post on Monday, sharing a photo of the siblings in their younger years on what looks like Christmas morning. Little brother Jansen sits on Hayden's lap in front of their festive Christmas tree, surrounded by presents, wearing a red sweater with Santa Claus on it. Hayden pokes her head out from behind him, flashing a big grin for the camera.
Jansen was found dead on Feb. 19 in his New York City apartment. He was 28.
At the time, a source told ET, "Hayden is absolutely heartbroken. She loved her brother unconditionally and the two shared a special bond."
In a statement to ET, the Panettiere family, including Hayden, and their parents, mom Lesley Vogel and dad Skip Panettiere, shared the cause of death for Jansen.
"Though it offers little solace, the Medical Examiner reported Jansen's sudden passing was due to cardiomegaly (enlarged heart), coupled with aortic valve complications," the family said.
"Jansen’s heart could be seen in his eyes, and his charm in his brilliant, engaging smile; his soul in his masterful and revealing paintings, and the joy of life in his dry wit," the statement continued. "His charisma, warmth, compassion for others, and his creative spirit will live forever in our hearts and in the hearts of all whom he encountered."
"He’s right here with me," Panettiere tearfully said at the time.
Like his sister, Jansen was an actor. He had several film and TV roles throughout the early 2000s, with credits on Even Stevens, The X's, Tiger Cruise, Racing Stripes, The Martial Arts Kid, The Walking Dead, Perfect Game and How High 2. His most recent role was in the 2022 Christmas film, Love and Love Not.