"Thank you for all of the kind words and love that has been sent my way," she began in a message she shared on her Instagram story on Friday.
"I have been at a complete loss," she continued. "Nothing about the past few days have felt real. I ask and pray that you'll give me the grace and space to navigate this in private."
She then said, "Liam, my angel. You are everything. I want you to know I loved you unconditionally and completely."
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"I will continue to love you for the rest of my life," she added. "I love you Liam."
Payne died at age 31 on Oct. 16 after falling from the third floor of his hotel room in Argentina, according to state police. Payne's body was found in the inner courtyard of the hotel, where he was pronounced dead on the scene.
The English singer was 31.
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Cassidy and Payne had been linked since 2022. They made their official red carpet debut in December 2022 at the Fashion Awards in London.
Cassidy frequently shared photos of her and Payne together on social media throughout their relationship. She explained how they met in a TikTok video posted in September.
In the video, Cassidy detailed meeting Payne while working at a bar in Charleston, South Carolina. After their initial meeting, Payne and Cassidy had lunch and bowled together in Charleston, according to Cassidy. "He ended up staying in Charleston for three days past his original flight," she said, adding at the end of the video, "Everything happens for a reason."
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Liam Payne death: Former One Direction singer dies after fall from hotel in Argentina at 31
Payne also frequently appeared in Cassidy's TikTok videos. In early October, Cassidy posted a TikTok video with Payne where she hugs and kisses him on the cheek. The month before, she shared an image of them attending a wedding together in Paris.
Cassidy also showed her love for Payne in an Instagram post in August last year when she celebrated his 30th birthday with a sweet tribute. "30 never looked so goodhappy birthday love," wrote Cassidy. The post included several photos of the pair smiling, posing together and holding hands.
Cassidy has over 300,000 Instagram followers and 400,000 TikTok followers and frequently shares photos of her travels around the world.
Payne was previously engaged to Maya Henry and shared a 7-year-old son, Bear, with ex-girlfriend Cheryl Cole.