Applicator system for a hair treatment device, comprising: - a reservoir containing a cosmetic product, - an applicator comprising a body in which an application member made of a porous material partially extends, the applicator being arranged to be removably attached to the reservoir so that the application member comes into contact with the cosmetic product contained in the reservoir and is refilled with cosmetic product, the applicator being configured to be removably attached, after separation from the reservoir, to a corresponding receiving zone of the hair treatment device, the amount of cosmetic product initially contained in the reservoir being greater than the amount of cosmetic product transferred to the application member during the refilling of the latter by the reservoir, the application member comprises an application surface, extending outside of the body, and configured to be brought into contact with the hair when the applicator is removably attached to the corresponding receiving zone of the hair treatment device, the application surface extending in the reservoir when the applicator is attached to the reservoir, the applicator comprising an attachment relief configured to engage with a complementary relief of the corresponding receiving zone of the hair treatment device. - a reservoir containing a cosmetic product, - an applicator comprising a body in which an application member made of a porous material partially extends, the applicator being arranged to be removably attached to the reservoir so that the application member comes into contact with the cosmetic product contained in the reservoir and is refilled with cosmetic product, the applicator being configured to be removably attached, after separation from the reservoir, to a corresponding receiving zone of the hair treatment device, the amount of cosmetic product initially contained in the reservoir being greater than the amount of cosmetic product transferred to the application member during the refilling of the latter by the reservoir, the application member comprises an application surface, extending outside of the body, and configured to be brought into contact with the hair when the applicator is removably attached to the corresponding receiving zone of the hair treatment device, the application surface extending in the reservoir when the applicator is attached to the reservoir, the applicator comprising an attachment relief configured to engage with a complementary relief of the corresponding receiving zone of the hair treatment device. the amount of cosmetic product initially contained in the reservoir being greater than the amount of cosmetic product transferred to the application member during the refilling of the latter by the reservoir, the application member comprises an application surface, extending outside of the body, and configured to be brought into contact with the hair when the applicator is removably attached to the corresponding receiving zone of the hair treatment device, the application surface extending in the reservoir when the applicator is attached to the reservoir, the applicator comprising an attachment relief configured to engage with a complementary relief of the corresponding receiving zone of the hair treatment device.