I’ve never seen a mature Lakeside Shore Master but this one reminds me of it. I have a youngster but the medio-variegation runs right to the tip like LSM does.... your f-i-l’s colours (lots of shade?) are very deep - beautiful!

I’m also staring at Great Expectations in my yard and imagining it dark like that in deep shade, lol.

Could possibly be Dream Weaver. (Of course, Dream Weaver, Dream Queen and Thunderbolt are almost identical.)

I thought Dream Queen as I am wanting to purchase one myself. The photos of DQ seem to show a narrower stripe down the leaf. But.....?

Great Expectations in that much shade would probably not get that large, and it's too dark. Even in a lot of shade GE has brighter coloration, but does not grow much. Same for DQ and DW, both GE sports. Thunderbolt is a sport from Elegans, but also does not thrive in full shade, and has lighter coloration.