In the video Anthony said: “What’s happening Reece, I hope you’re well champ?
“I just want to say keep fighting, keep strong.
“I spoke to the team and they passed on your message so I wanted to get one back and say god bless you, take care.”
Reece, 12, from Overton, was diagnosed with Malignant Anaplastic Astrocytoma, a rare brain tumour nearly two years ago.
The tumour affects only about 10 children a year.
A friend of the family, Mick Kirk got in touch with Anthony Joshua.
Since his diagnosis Reece and his family have received an immense amount of support and are amazed over Anthony Joshua’s comments.
“Reece is absolutely amazed that Anthony would even know who he is never mind take time out to send him a message, it’s really lifted him,” said mum, Rachel O’Neil.
Mick was a former boxing coach at Finchley & District Amateur Boxing Club and his son, Owen has also boxed there.
Anthony Joshua trains at Finchley and Mick and friends have been trying to get hold of Anthony.
Mick said: "We have been tying to get some of the guys at Finchley to grab AJ for a while when he pops in to see the boys and train with them.
"It was only by chance my son saw him and he did a live feed whilst at Finchley and he called one of the coaches immediately and asked him to send the message, and here we are, he did it without hesitation!
"We tried a few months ago after we produced the Everybody Hurts charity music video to arrange a FaceTime between AJ and Reece but given his training schedule it proved difficult.
"We are pleased for Reece we could make this happen and really glad he liked it."
Reece announced his brain cancer was terminal on his Facebook charity page, Team Reece in February.
Following the terminal diagnosis, Reece and Rachel are continuing to work hard for Team Reece.Read more about Reece here.