How do I straighten a fence post?

I have a fence about 15 years old. I concreted in the corner posts and those on either side of the gate, but this non-concreted one has leaned. I've thought about either digging around it and adding concrete, but getting to the right depth of at least 4' (I'm in SW Ontario) would be very difficult with the fence in the way. I could put in a new post right next to it, but that would only be concreted on one side. Alternatively, I could put in a new post a foot away and brace the first one. This would be easiest, but not visually the best. What would you recommend, please?