"The show was fantastic!" Mallette enthusiastically says in the video, later laughing when plenty of fans began pointing out the 36-year-old reality star's presence.
Last November, Bieber blamed his deteriorating relationship with his mother on his headline-making bad boy behavior.
"I was distant because I was ashamed," he told Billboard. "I never wanted my mom to be disappointed in me and I knew she was. We spent some time not talking, so it takes time to rebuild that trust."
"She's living in Hawaii now, so it's hard, but getting better," he added. "She’s an amazing woman and I love her."
Mallette, who gave birth to Bieber when she was 17 years old, wrote a best-selling book about her struggles growing up -- 2012's Nowhere But Up. ET caught up with her in February 2013, when she admitted that she wasn't always a fan of her superstar son's life choices, particularly, his multiple tattoos.
"That's one of those things that I don't necessarily have to like," Mallette said, also acknowledging at the time that her son is legally an adult. "He's going to make his own decisions."
... But would Mallette approve of Bieber's "drunk" rant during his impromptu performance at 1OAK nightclub in Los Angeles the night before his Staples show? In video footage exclusively obtained by ET, Bieber, 22, appeared to be tipsy and took a seat on the DJ booth to address the crowd.
"I think people hate on people who are themselves, you know?" he said, slightly slurring his words. "Maybe I'm drunk or maybe I'm just speaking real s**t, but I feel like a lot of the reason why there's so many people that hate on me is 'cause I'm just myself."