Answer:
We will not know immediately
Step-by-step explanation:
The distance of star Betelgeuse = 325 light years
Therefore, if it where to explode, at the location, we would have a supernovae such that the luminosity of the star multiplies several multiple times
However, due to the distance of Betelgeuse from the Earth, it will take the light of the explosion, 325 years to reach Earth and the explosion as it happens will not be noticed here on Earth immediately