Chad Lowe's eldest daughter mourns loss of younger sister, Fiona

Chad Lowe’s daughter, Mabel, has shared a heartfelt tribute to her younger sister following her death this week.

Fiona Lowe passed away earlier this week and it later emerged the 13-year-old had taken her own life, and now Mabel Lowe, 17, has pledged to "honour" her beloved sibling "forever."

Sharing a number of throwback photos on Instagram, Mabel wrote, “I love you so much Fiona.”

“I wish your short time here was easier and I hope your mind is at ease now. I will honour you forever and keep your memory alive. I love you, I hope you knew just how much,” she further expressed.

Pretty Little Liars actor Chad and his wife Kim Painter - who are also parents to 10-year-old Nixie - announced the sad death of Fiona earlier this week.

Remembering her as "a loving young girl who was smart, creative, and loved to dance", the family said in a statement to PEOPLE, "We are deeply heartbroken by the loss of our beloved Fiona. She was adored by her sisters and she was deeply loved by her parents. In fact, she was the light of our lives.”

"Her passing is devastating for our entire family and we ask for prayers and privacy at this time,” the grieving couple requested.

Last year, the Life Goes On actor, who won an Emmy Award for his supporting role in the drama series, took to social media to celebrate Fiona turning 13 years old.

Chad Lowe posted a picture of his beloved daughter on Instagram, and wrote in the caption, "Celebrating Fiona officially becoming a teen today!! Keep dancing through life FiBear! Love you soooo much!! (sic)"