In The Last Jedi, we see a flashback of:
Ben Solo waking up with Luke Skywalker standing over him with his green lightsaber ignited in his hand, and then ignites his own blue lightsaber in fright.
There are plenty of questions and answers about Kylo Ren's spitting red lightsaber with the vents because it's an imperfect Kyber crystal (also the impressive look), but is there any canon information about what happened to his original lightsaber?