The Blackhall five-year-old - who is fighting brain cancer neuroblastoma - has started the gruelling second stage of pioneering treatment after going back into hospital on Monday.
The family had been warned that the antibody stage of the combined therapy, which started yesterday, was likely to be tough because of the side effects expected.
Now Gemma has posted a picture of Bradley on the campaign Facebook page ‘Bradley Lowery’s Fight Against Neuroblastoma,’ and shared the family’s anguish at his suffering.
“It has been tough going since the antibody went up yesterday. Bradley has suffered from extreme pain and we have struggled to get it under control,” she said.
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“He had a really bad night so he didn’t get much sleep. Today has been slightly better, however, the pain still comes and goes.
“We expected this as it is one of the side effects from the treatment, however, watching my brave boy scream in pain is horrendous and nothing could prepare me for it.
“Please pray for our superstar that the pain stops and he gets that beautiful smile back.”
Bradley was initially diagnosed in 2013 and underwent chemotherapy before being given the all-clear a year later.
Sadly doctors found cancer again during one of his check-ups and an amazing £700,000 was raised to cover the cost of treatment in America, including a £200,000 donation from Everton football club.
The Merseysiders also invited Bradley to be their mascot for the game against Manchester City at the weekend, when he was carried on to the pitch by striker Romelu Lukaku.
He wore his Sunderland strip, with “Thank you Everton” on the back and reappeared at half-time, changed into an Everton strip bearing the slogan “cancer has no colours”.