When he was just 18 months old he was diagnosed with stage 4 high-risk Neuroblastoma and fought with all of his heart against the disease. Thinking of your mummy, daddy and all of your family at this very sad time.
During that previous spell with the Cherries - in which Defoe scored in 10 successive league games - he played alongside and was captained by Howe.
The Facebook page had earlier updated their profile picture to one of Bradley looking smart in a waistcoat and tie with a massive grin on his face.
The young football fan recently held a 'bed party' giving his loved ones, including Defoe, a chance to say goodbye. "Then the cameras came out and he was smiling".
Scotland and Stoke City midfielder Charlie Adam paid tribute on Twitter, saying: "He was a little fighter".
"Bradley's story not only touched our club and our fans, but also the wider football community".More news: Tour de France stage ends in impossibly close photo finish
Sunderland said Defoe was "heartbroken".
In particular, he received support from Everton, the club pledging £200,000 towards an appeal to pay for groundbreaking treatment in the United States last year.
"The thoughts of everyone at #afcb are with the Lowery family and their friends at this difficult time".
Though, there will be plenty he already knows too - that the squad is woefully short of experienced players ahead of the Championship campaign and strikers.
When a request was made by Bradley's mother and father to send him Christmas cards, it was answered by 250,000 people. The footballer had signed with another club based in the south of England but returned to the north to visit the child.
AN EMOTIONAL Jermain Defoe was reduced to tears whilst speaking about terminally-ill Bradley Lowery. Doctors found that his cancer had grown before informing his family that it was terminal.
The Black Cats conceded twice inside 30 minutes as Andrew Tutte and Callum Reilly took advantage of sloppy defending to beat goalkeeper Vito Mannone. I will miss you forever kiddo. Bradley genuinely lived life and he won't ever be forgotten.
Bradley, his parents and elder brother recently enjoyed a final holiday together on the Yorkshire coast, where they were welcomed by visitor attractions such as Scarborough Sea Life Centre. "Rest in peace, Bradley Lowery".