The 18-year-old was found dead at her home in west London following a suspected heart attack.
One Direction star Louis, 27, cancelled his planned performance on Comic Relief just two days later, with reports saying he is ‘obviously distraught’ at the devastating loss.
Now his 20-year-old sister Lottie has shared a heartfelt post on Instagram, admitting she feels ‘empty’ without her ‘baby sister’.
Alongside a series of sweet childhood and recent photos of her and Félicité, Lottie wrote: ‘My Fizzy, my baby sister, my best friend.
‘I’m incomplete without you, I’m empty. I can’t picture my life without you.
‘I wish we could have lived life together for a little longer.
‘Mama needed you and you needed her, you’re finally together again. I love you always, Dotty x.’
Félicité’s death came two years after the family were left distraught by the loss of their mother Johannah Deakin, who died in 2017 following a battle with Leukemia.
Louise and Lottie’s younger sister, Daisy, 14, was the first family member to break her silence with a tear-jerking message on Instagram.
‘This is the fourth time I’ve tried to write this,’ she penned on Sunday.
‘No words will come close to explaining how broken I am, once again. My precious sister. My heart is bleeding. I keep imagining and praying they have the wrong person. Not my sister, not my best friend.’
Referring to their mother, Daisy added: ‘Mama needed you. I hope you are happier up there with her. Make sure you don’t forget about us. Keep us in your conversations.’
Daisy’s twin sister Phoebe also took to social media with a poignant message, saying the family is ‘shocked and broken hearted’ following the death of Félicité, who was known as ‘Fizzie’.
She said: ‘You were my best friend, sister, motivator and person that could make me laugh until I cried.
‘I’m lost without you and the thought of never seeing you again scares me like you wouldn’t believe.’
Concluding the heart-rending message, she added: ‘Mummy needed you and you desperately needed her. I’m so glad your together now and she has you to rub her feet in heaven like you used to. I pray that you’re in a better place now.’