The 36-year-old comedian, who filed for divorce from the singer in December 2011 after 14 months of marriage, is said to have changed his mind after seeing photos her at Coachella Festival last month.
Perry, 27, was spotted being affectionate with Robert Ackroyd from music group Florence + the Machine as they watched acts on stage.
According to Grazia, Brand was prompted to admit that he “gave up” on their marriage too soon and that filing for divorce was the biggest mistake of his life.
“Word has it Russell was ‘seething with jealousy’ when he saw pictures of her with Rob,” Contactmusic quoted a source as telling the publication. “He apparently feels he gave up on their relationship too easily.
“It’s fair to say that Russell only wishes Katy happiness but perhaps he should have realised just how special his wife was when he was married to her rather than five months later,” the source added.