Holey Moley I can only guess a mole or other burrowing animal got to the root of  the lily. This has also happened to my own lily bulbs. I suggest you cut the stem of blooms to try and revive them by placing in a vase of water. You can feel the soil around the bulb for a tunnel and flood the soil with water to try and collapse any mole tunnels  that are drying out the roots. If you leave the foliage of the lily to mature this summer your bulb will most likely survive and you can enjoy those beautiful blooms next year. So sorry about the loss.  Keep growing, Marianne Binetti