Matthew Rowley visited sibling Charlie in hospital as he continued to recuperate following exposure to the nerve agent novichock.
“It was very upsetting,” he told Sky News, shortly after the visit.
Matthew, who says he and his brother are Catholics, said: “I said a prayer for him last night.”
“We had a little chat,” he said, adding that his brother “wasn’t himself”.
“It was quite upsetting actually when I walked in to see him in the condition he’s in,” Matthew said, noting that his brother has been unable to eat for a number of days and was having to rest his head on a pillow.
He continued: “He was struggling to make himself upright… he’s got loads of machines everywhere and so many tubes and wires coming out of him..
“At least I’ve seen him now… he’s not out of trouble yet but hopefully he’s going to get better but they can’t say yet.
“He’s going to be in there for a while.”
Mr Rowley, 45, was left in a critical condition and Dawn Sturgess, 44, died on Sunday evening after they were poisoned by the substance.
Asked about whether his brother is aware of Ms Sturgess’s death, Matthew said Charlie was “very upset. I’d say he’s more angry than upset.”