5 year insisting he doesn’t love his grandma

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My mom lives with us. She has been a parent of my sons life since he was baby as she was his primary caregiver when my husband and I are work. He has always loved her and for a lot of the time preferred her to my husband and myself. He recently turned 5 and the past few weeks has been saying how he doesn’t love her anymore and I don’t like her. I told him how much his grandma loves him and he said that he doesn’t love her back. He will have a tantrum if he has to stay with her. I’m concerned. He has gone through phases where he didn’t like one of us but always got out of it. He says he only likes me. I asked him why he feels this way and he said because she’s just gray. I’m not sure how to navigate this. My mom and husband aren’t the best friends and there is some tension between them so I am wondering if he is picking up on that. Any advice would be great.