It's not a problem if only the final chapter does this.
As Amadeus mentions, chapter length is a kind of unspoken pact with the readers. If your chapters are somewhat even around 2k words, most readers will expect another 2k words.
Maybe coming into the final chapter they'll wonder, "hey, how is this going to sort itself out in such little space?" just to discover that the final chapter is thrice as long. But if the quality of your writing is good, and if the ending is compelling, there is no major issue in that. Readers that followed you up to that point won't drop your book at last.
It's a once-in-a-while exception to the unspoken rule, and it will be forgiven since it's the last chapter.
While this is true, it may be worth splitting it, since you already found a good turning point, or a good cliffhanger. If your story is compelling, it will make no difference. Dedicate readers will go from the second-last chapter to the final one without even noticing the split.
The plus side here is that you're giving your audience a choice. Maybe having a clear-cut break point will be useful for those readers who don't like reading all in a bulk. Maybe some of them don't have enough time to face a 7k chapter. You'd be providing a nice place to stop, a place where it makes sense for the plot, also, and sparing them the hassle of having to find a break themselves in some arbitrary point.