Mysterious wet patch on newborn

I let my newborn lie on a flat surface and noticed a wet patch on his back. Don’t think it’s pee or sweat. It’s colourless and odourless. Anyone encountered the same thing? Can share what is it? Thank you! 🙏 Update: It is pee! I was about to change the diaper and saw the pee flow out from the gaps of the diaper 😂