Which are the three cells found in a pollen grain when it is shed at the three celled stage?

one vegetative cell and two male gametes

Explanation: In over 60 % of angiosperms, pollen grains are shed at this 2-celled stage namely vegetative cell and generative cell.

In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed. This is 3-celled stage i.e., one vegetative cell and two male gametes.