Small Engines (Lawn Mowers, etc.): Mower Blade not working properly, key way, center hole

Question
I have a
Toro,  22" , front drive,  6.5 HP Recycler mower
Model: 20016
SN: 220338372

At the end of the season last year, the mower started to vibrate, then the blade stopped turning  at the speed of the engine. ( It did not strike anything.) I examined it, confirmed that the blade is loose and  is turning independently of the shaft. I see no evidence of a "key way".

The shaft seems to be still fixed in place to/in the engine.

What's the likely diagnosis?
Thank you for your consideration.


Answer
William
Seems to me that the blade came loose out of the mower because it may be unbalanced,that will cause vibration.Never run the mower with out the blade on as this will damage the engine.There is no key way other that the blade may have a star in the center hole or another shape to seat the blade. Buy a new blade and install it but first have a dealer look at the blade and check for balance.