How do I ask my unhygienic housemate to move out?

Some context: I was entrusted with living in and looking after my aunt’s house for a number of years now, and I’ve been subletting a couple of the rooms to help pay the rent and bills. One of the rooms is vacant, so I only have one housemate now who’s been living here for about a year and a half.

My housemate is a very friendly and nice guy, but I’ve come to discover some alarming things about his personal hygiene and cleanliness. Some things that have stood out so far is that there is a smell of rancid sweat that comes out into the hallway from his room. In the 3 months of lockdown, he has only done 5 washes of his clothes (my room is under the washing machine so I can always hear when its on). He appears to not use the handsoap after using the toilet, as there have been periods of time when its run out and he hasn’t replaced it, yet obviously has still been using the toilet. He has frequently gone days without showering, which at one point where he was working from the lounge caused such a stench that I couldn’t enter it without the smell being there for days. He put a half eaten tin of beans into his cupboard, completely open, which I only discovered because I could smell rot and mould in the kitchen. The list goes on, but ultimately I’ve come to the understanding that hygiene and cleaning in general doesn’t matter to him.

Just before lockdown began, I sat him down and tried to speak to him about it. Given the need for us all to be more hygienic during a pandemic, I asked him to shower at least once a day and that as part of the lease and me caring for my aunt’s house, he is expected to keep his room clean. He was quite defensive but that day he went for a very long shower and cleaned his room, leaving the door open and lighting a scented candle. I was hopeful this would be a turning point for him and that it would be solved – however whilst he seems to have kept showering (as far as I can tell, but I don’t spend a lot of time around him anymore), the hallway is beginning to smell of his room again. As he keeps the door closed at all times, and seems to avoid going into it whenever I’m around, I can’t tell what the state of it is in.

I’m starting to consider letting out the vacant room again, but I can’t in good conscience let someone move in with the smell of his room permeating the hallway. I’ve come to the conclusion that I must ask him to leave, but I’m not sure how to in a way that won’t hurt his feelings. I’ve moved past wanting to get him to change his behaviours because its obvious that this is his lifestyle and its not my place to change that – but if it wasn’t my Aunt’s house I would have already been considering moving out because of it. I have a strong suspicion that the previous housemate left because of it too.

One thought I had was to ask him to leave on the basis that I would like to live alone – however this would be a lie, as whilst I could cover the full rent for a month or two, I would eventually need to let out the rooms again and this is something I’m keen to do soon.

I feel like not giving him any explanation would be unfair. So, how can I ask him to leave based on not following the request to improve his cleanliness?