How do I get him to brush his teeth??

21f 23m in a relationship for nearly 4 years, I’ve been having this problem that I’ve only really started to notice in the past year, my boyfriend like never brushes his teeth and I don’t know how to tell him to start brushing them without embarrassing him or making him uncomfortable, I’ve started going in the bathroom while he is using the toilet to brush my teeth to hopefully entice him to brush his and it works sometimes or I buy new toothbrushes to give him but I buy weird looking ones so he will be more intrigued to try it?? Idk, when I started realising this I thought I would try find out how long he goes without brushing his teeth so I hid his toothbrush and didn’t tell him…. A month passed and he didn’t notice, it’s just so annoying because he’s the best boyfriend you could ask for, he treats me really good and he loves me so much I can see that he does, we never argue likes ever, we do have some disagreements over silly things like how a word is pronounced but we have never shouted at eachother, and the most annoying thing is he’s really hygienic in every other way apart from oral hygiene like he showers 4-6 times a day and loads of other good hygiene things, I can’t kiss him because it grosses me out that his teeth are never clean and he asks why I never kiss him anymore and I tell him his breath smells bad and he just says sorry instead of going and brushing his teeth, do I just straight up say “brush your teeth” I feel like that’s too harsh, i would be so embarrassed if he had to sit me down to tell me my breath stinks and I need to start brushing my teeth, has anyone else ever had this problem and if so how did you fix it?