So it's probably coming from prostate, or urethra just below the lower sphincter.
This would not be surprising as a result of RT damage to blood vessels, which can take 1-5 years to fail afterwards. Peak period for late bleeding from rectum is 4.5 years afterwards, which is how long those blood vessels take to fail after RT damages them.
Normally all that's required is to get the cause confirmed, and if it is this, no treatment is necessary in the case of rectum - it fixes itself. I don't know as much about it when it's the urethra, but it's probably similar.
In any case get it checked out, just to confirm it's not something more serious.