Ceiling Trouble / Bathroom Leak

[Jacob Kurian]

Hello, I am a first time landlord with my first property. My tenant just notified me of this in November and they first started noticing it back in May (eye roll lol). There appears to be a leak but I'm not a very handy guy and am not 100% sure. The images are from the living room ceiling. Right above it is a bathroom. Does anybody have any advice on alternatives to resolve or get this fixed before I go all out & call a plumber. They'd likely charge a premium, which would hurt my numbers on my first property. If anybody has any cheaper, alternative options to try first before resorting to a plumber and killing my CAPEX reserves, it would be greatly appreciated! I've attached some pictures to my post of the issue. Thanks in advance!