Bradley, aged six, was diagnosed with a neuroblastoma in 2013 and the Lowery family were informed their son's condition was terminal in December 2016.
Aside from being a massive Sunderland and England fan - Bradley was the team mascot as Defoe accompanied him onto the pitch - it's clear that the new Bournemouth striker became an incredibly close friend of Bradley as seen by the emotional interview that he gave recently.
In a statement posted on his official Twitter account, Defoe said: "Goodbye my friend, gonna miss you lots". I feel so blessed God brought you into my life and had some wonderful moments with you and for that I'm so grateful.
"I'll never ever forget the way u looked at me wen I met u for the first time, the genuine love in those cute eyes". Really finding it hard to find the words to express what you mean to me.
'Your courage and bravery will continue to inspire me for the rest of my life.
Malaise cardiaque d'un joueur de l'Ajax en plein match
L'Ajax a communiqué il y a quelques minutes en indiquant que l'état du joueur était "stable". Le Néerlandais de seulement 20 ans s'est brutalement écroulé sur la pelouse.
Lowery also was a mascot for an England game at Wembley Stadium in March, and supporters of different clubs made banners and chanted his name at games. God has you in his arms and I'll always carry you in my heart.
'Sleep tight little one.
Since the sad news broke, Bradley's parents released a statement which read: "My courageous boy has went with the angels today 07/07/17 at 13:35, in mammy and daddies arms surrounded by his family".
The statement said "he was our little superhero and put the biggest fight up but he was needed elsewhere".
"Her words were so incredible that she lifted the girls on a high, they were so overwhelmed with what she had said - that our Bradley would be with them and always in their hearts and head he will always look over them and when they see a white feather they will know he was there". Thank you everyone for all your support and kind words.
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