The First Doctor and The Doctor in “Twice Upon a Time”

What's the matter?

I died a few hours ago and I refused to regenerate. Catches up with you, you know. It's like a big lunch.

I did exactly the same.

I know you did, but why? I don't remember this. Why are you refusing the regeneration?

Fear. I'm afraid. Very, very afraid. I don't normally admit that to anyone else.

Don't worry. Technically, you still haven't.