My Oldest Son continuously being annoyed by my younger son; oldest started crying uncontrollably today because the younger was being annoying

Jul 2021
United Kingdom
The title explains most of what this post is about.

Longer Story
Yesterday, my youngest son was being highly annoying to the entire family.
This morning, when my oldest son woke up, he was in a very bad mood, which he later claimed was due to his younger brother.
Anyway, I left the house before either of my sons had woke up and got back at roughly 1PM.
When I got home, I could tell my oldest son was in a bad mood and when asked what was wrong, he said that he was highly annoyed with his brother and he then started crying uncontrollably.
He’s never done this before.

Should we be worried?
Jul 2021
Re-assure them that they are really okay.
In their okayness there is no fear if things don't go their own way (not God's way). To realize one's okayness helps them to see that their is no need to be in a bad mood, be annoying, or wanting the other person to be nice to them. Okay people live and let live. . . they become unconditional, not conditional.
Unfortunately most other people don't know how to cope with life's non-okayness. Those lacking coping strategies around them (school, etc) tend to be their role models. Home is their haven, and main reference point on how to cope, with self, whenever they don't feel okay.