Sentence:  I was about to say that I had known the Celebrity from the time he wore kilts. But I see I will <WSD>have to</WSD> amend that, because he was not a celebrity then, nor, indeed, did he achieve fame until some time after I left New York for the West. 
Meaning of the word marked with <WSD> tags:  Must; need to; to be required to. Indicates obligation.