Chivas Regal Scotch Whisky Question

I am not a big Whisky drinker but have a question about something I found today. My Grandfather passed away 23 years ago. While looking around in his old bar which has been untouched for that long, I found a couple bottles of unopened liquor. One of the was a 12 year Chivas Regal Scotch Whiskey. Given that he has been dead for 23 years plus it's 12 years aged, it's a least 35 years old.

Can anyone tell me if this is worth anything and what the quality night be like if I opened it

Thanks