I am using BibTeX with `natbib`. My style file orders my bibliography in the order in which articles were cited. Occasionally, however, I want an `\cite` to be ignored for the purposes of the bibliography order, but fully working otherwise. 

Minimal working example:

```
\documentclass{article}
\usepackage[square,numbers,sort]{natbib}
\begin{document}
\cite{c} % Want to cite, but ignore for purpose of bibliography order.
\cite{a}
\cite{b}
\cite{c}
\bibliographystyle{unsrt}
\bibliography{ex}
\end{document}

```

with ex.bib:

```
@article{a, author="a"}
@article{b, author="b"}
@article{c, author="c"}

```

results in:

![enter image description here](https://i.stack.imgur.com/lXNFH.png)

as expected. I want to replace that first citation with a new command, say `\ignorecite` so that the order is `a,b,c`, and so that the order in the main document is `3,1,2,3`