Microsoft Excel Column Headers Showing as Numbers Instead of Letters

I had a strange occurrence recently with Microsoft Excel where the column headers changed from letters to numbers. I’d didn’t notice initially, but it was when I was working with a formula that I realised it wasn’t putting letters in the cells but an odd numbering style.

When I looked into why I discovered the column headers were numbers:

I did some digging and found an option on the Formulas tab called R1C1 reference style was marked:

I unmarked the option and saved the options; when I closed them and returned to the main Excel window, the column headers were again as I was used to with letters:

I’m not sure why or how this setting had been enabled, but at least I can easily find it next time should the same recur.