Help me find this one pls!

I loved this one, it was about someone`s grandson becoming a zookeeper and the zoo was full of mythical creatures like mermen and a plant creature??? pretty sure the main love arc was his colleague actually being immortal or smth, watching over him because of the protagonist`s grandfather originally being together with the immortal guy. Many thanks in advance i have searched every single page for this and have not found it, Your a liversaver!