I have 2 close together (22 month gap) then a 9 year gap to the third.
Like you, it was unplanned, I had previously wanted a third, but had decided against as the others got older.
My DH was very against the idea of this unplanned DC3, and went so far as to threaten to leave if I kept it. I did consider terminating the pregnancy (not because of his threats, but because of my other 2 children, job, age etc etc)
I went for a dating scan and was much further on than I had thought, so a termination was not possible.
My older kids love their little brother in short doses, and are great at practical help, they will babysit now (they are 16 and 14) and drop him off /pick him up from school.
I do think my life would have been a lot easier if he hadn't arrived, e.g. all fitting in the car, booking holidays and days out etc, but we all love him to bits and wouldn't be without him now. - DH got over his shock, and the completely crap way he reacted to it, and is now (time wise) the main child carer, works pt to fit around school etc.