Eric O'Hara, 24, was working on the roof of the Steamboat Grand Resort Hotel in Steamboat, Colorado when a piece of ice broke loose and he fell off the building.
O'Hara had been home just a month since serving as a member of the 82nd Airborne Division in Iraq and Afghanistan over three years.
"I just loved him more than anything," Montag told Usmagazine.com. "He couldn't wait to meet Spencer."
"He was very much a brother to me," she said. "He called me his sister, not his step-sister. He was always like, 'I love you! I have to meet Spencer and make sure he's cool to you!' Just like a brother."
Montag's father, Bill, married O'Hara's mother, Terri, when Montag was 7-years-old. Montag lived with her mom and O'Hara lived with her dad. She saw him every weekend, at holidays and during the summer.
"He was just back [from Iraq] and was ready to go back to school," Montag explained. "He went up to Steamboat for the weekend where my dad lives."
"He was just so patriotic," Montag told Us. "He just really wanted to go there and help and do all that he could for his country. He felt like it was his duty."