It comes after the family lost their mother Johannah Deakin in 2016 from leukemia.
Louis, who is working in London at the moment, is "devastated and distraught," by the death of his young sister.
A source close to the family has revealed that “Félicité was an absolutely adored young woman who was loved by Louis and her whole family.
“They are all totally devastated, as you can imagine.
“She had so many friends and was such a positive happy person. It’s a massive loss to the world.
“She was a loveable, caring, bright, passionate, popular and beautiful young lady.”
Our heart breaks for the Tomlinson family. Our thoughts and prayers are with them all during this difficult time.