The singer, who was fatally shot at her concert Friday night, worked side-by-side with her brother

By Julie Mazziotta
Updated June 11, 2016 06:10 PM
Source: Mark Grimmie/Instagram

Christina Grimmie‘s close, “loving,” relationship with her brother Marcus, who tackled her gunman after she was fatally shot at her concert Friday night, was clear, a source tells PEOPLE.

“It was obvious that they had a really loving relationship,” says the source, who worked with Christina and Marcus on a video performance. “You could tell they had each other’s backs.”

Marcus, who also goes by Mark, served as Christina’s tour manager, and “was like her right-hand man,” says the source.

“They basically hung out the entire time,” during the shoot. “You could tell they were sort of a team. There was a lot of laughter in between takes, during takes – they were joking back and forth. It was a really good vibe.”

“You could tell he really cared about her and her career. It was sweet to see, knowing they were siblings.”

Christina was talking to fans at a meet and greet after her performance in Orlando when Kevin James Loibl opened fire, killing the Voice alum. Marcus “almost immediately” tackled Loibl, according to police, and Loibl then took his own life.

Orlando police chief John Mina praised Marcus for his bravery in the moment.

“Very heroic actions by Marcus to jump in, and definitely could’ve prevented further loss of life,” Mina said in a press conference Saturday morning.

Marcus posted on Facebook Saturday afternoon thanking everyone for their thoughts and prayers.

“Christina was more than my sister. She was a partner in life. A superstar. A goofball. Introverted. And a friend to everyone. Genuinely,” he wrote. “But above all…she was my baby sister. She loved the Lord and her family and was always there for me and I honestly don’t know what ill do without her.”