In her open letter, she wrote: "I first met you in 2004 for the 46664 AIDS Benefit Concert in Cape Town, and the impact you have had on my life resonates with me today and every day. Your kindness and gratitude for every experience and your ability to forgive are lessons I have learned and will pass on to my three children. My entire family holds you in high regard.
"It is an honour for me to travel to South Africa this week in celebration of you and your efforts to right so many wrongs. You were a strategic warrior, a bold activist, and charismatic and well-loved leader.
"Your vision for dignity, for human rights, for peace and a South Africa free of racism and apartheid, allows us all to turn dreams into reality. You made it possible for so many people like me to reject impossibilities and understand our capabilities in making lasting change in the world. The smallest efforts could change the trajectory for so many living in extreme poverty, facing injustices, the indecency of racism and fighting for their rights as humans."
And the 37-year-old singer, who penned the letter ahead of the Global Citizen: Mandela 100 concert, which will take place on December 2 in Johannesburg, South Africa, at which she will perform, has promised Mandela his "sacrifices were not in vain".
She added: "As we celebrate the Global Citizen Festival: Mandela 100, honouring your centennial year, I promise you that we have made your dreams our own. Your work and your sacrifices were not in vain. I will cherish every moment shared in your presence and use the lessons learned from you as fuel to stir positive ideas and solutions."