Help with plant ID please

[NotAnEMERGENCY]

I lifted this from a border in June (?) when it was absolutely tiny with only a couple of leaves just starting to poke out of the soil. I still don't know what it is. It's grown loads! Is it going to grow much bigger?

[Sosidges]

Looks like a Cordyline to me.

[NanTheWiser]

No, not a Cordyline - looks bulbous?

[shovetheholly]

Could it be an iris? The way it fans out reminds me of them.

[Trethew]

?? Sisyrinchium striatum

[shovetheholly]

Oooh Trethew, you're so brilliant at this!

[NotAnEMERGENCY]

Yes, having googled the images, I think Sisyrinchium striatum looks like the best bet. Thanks, everyone!