"He was an amazing guy," he said. "Everybody from school would talk to him."
He was also, his brother said, a gifted singer who had made demo CDs, hoping to turn his talent into a career.
When asked about Balbuena, Julio Valdivia said, "I don't want to talk about that guy."
Julio Valdivia, who also had Hofmann as a teacher, said he never had any inkling that she and his brother were romantically involved.
But Chandler police said there was evidence that Hofmann's interest in her students goes back a few years.
Chandler Police Sgt. Joe Favazzo told ABCNews.com that police found Hofmann and Balbuena together in a parked car back in 2006, but had no reason to charge her.
Balbuena, then 17, was a student at Marcus de Niza High School in nearby Tempe where Hofmann was his math teacher at the time.
"They were not doing anything," he said. "They were dressed."
According to the police report from November 2006, Balbuena initially tried to pass himself off as his 21-year-old brother Wayne. They told police that Balbuena was a family friend of Hofmann's and that the two had stopped on the street to empty an ice chest after attending a soccer game, the report said.
But upon being searched by police, Balbuena was found to be in possession of Hofmann's bra, according to the report. His explanation was that Hofmann had asked him to stow some of her clothes in the back of the car, but neither had an answer for why he was still carrying the bra.
Both were administered breath tests -- Balbuena had not consumed alcohol and Hofmann was under the legal limit -- and Balbuena's parents were called to pick him up. According to the police report, Balbuena's parents did not know he was with his teacher at that time, but that Hofmann had regularly picked him up to tutor him in math.
After the 2006 incident, Chandler police notified Marcus de Niza High School and shared a copy of the report with administrators.
A school district spokeswoman confirmed to ABCNews.com that Hofmann resigned from her job there in May 2007, but would not provide the reason nor comment on whether it had anything to do with the police report.
Jason Rusher, Hofmann's ex-husband, said he tried to warn judges during their divorce proceedings that she had allegedly been having improper relationships with her students.
"They didn't want to listen to me," he told ABCNews.com. "They thought I was nuts."
Their divorce was finalized about nine months ago, he said, and Hofmann's relationship with her students was a factor. Rusher said he had walked in on his ex-wife while she was having sexual relations with Balbuena.
Balbuena is next due in court on Thursday to enter a plea.