To think this ring has been changed

[Ondonotdisturb]

Long story short.. I was left a sapphire and diamond ring, I think the diamonds are original but family have a feeling a certain family member has swapped out the sapphire. I’ve cleaned it as best as I can and am able to shine a light from underneath which makes the gem shine green/blueish and appear murky. From above with no light the gem is very dark/almost black
wondering if anyone on here would be able to identify if this is fake or the original? There seems to have been some lighter blue stripes appear where I’ve maybe scraped the dirt from underneath (in first image) a little harder?

I'm a jeweller, specifically I work in the business in gemmology and valuations. Sorry, I've read your posts but not the the whole thread so it might have been said. Definitely needs to be taken to a jeweller to be certain, they could do a valuation for you that involves using different pieces of equipment to test it and not just looking at it. Australian sapphires are almost black, a lot on the market are dark blue/black. The four numbers will be an etched product code by the retailer, but it looks like you have a UK hallmark too. The lines you see are most likely natural inclusions. Do you think it was a brighter blue before? It's possible that someone could ask to change a stone, but it wouldn't be a particularly cheap thing to do so it wouldn't net them a lot of profit