Cannon, 33, and Carey have been leading separate lives for the last few months, reported Radar online.
"I did not know about it. We always stay in touch," Marie said.
The 'America's Got Talent' host had once posted a picture on his Twitter account with his grandmother when they reunited in May.
The father of three-year-old twins Monroe and Moroccan had also expressed that his daughter resembles the Cannon family matriarch.
"I'm shocked, I'm just so shocked. I know it's possible it could happen. People break up. People have problems," Marie said.