Thanks, BeeTee, you beat me to it. Piccie of the new 50€ note on the postoffice.co.uk
website along with a bit of info:
Can I still use the old €50 note?
Yes, you can. To use up remaining stocks, the European Central Bank will keep issuing old €50 notes alongside the new ones. So don’t be worried if you find both in your wallet.
The old banknotes are still valid, so you can keep using them.
"So don’t be worried if you find both in your wallet." Hm, finding 50€ notes in my wallet wouldn't worry me too