Killer Mike by Son's Side for Kidney Transplant Day After Grammys Arrest

Killer Mike's officially putting his arrest at the Grammys on the back burner, because after a long wait, his oldest son is finally getting a kidney transplant ... TMZ Hip Hop has learned.

Sources connected to the Grammy-winning rapper tell us Mike is with his son Mikael "Pony Boy" Render Monday as he undergoes the transplant surgery. The 21-year-old has been waiting for a kidney match for 3 years.

Back in November, Mikael got bumped up on the transplant waitlist, and his proud dad talked about it during an interview with Graham Bensinger.

Mike has said Mikael -- who's a musician and rapper, just like Dad -- never had a chance to fully experience his teenage years, because of his battle with kidney disease.

The fact Pony Boy's number got called for the transplant today, of all days, seems like a strange twist of fate ... considering his dad's weekend of some major ups and downs.

TMZ broke the story ... Killer Mike was awarded 3 Grammys Sunday at L.A.'s Crytpo.com Arena -- but he also got arrested.

He was booked for misdemeanor battery after allegedly knocking over a security guard at the venue, but was quickly released on his own recognizance. After getting released ... Mike was in relatively good spirits, even though he'd gone through a fairly dramatic situation.

Paps tried talking to him about it in the aftermath -- but he wasn't really trying to talk much about it ... keeping his attention on the music. In light of this news about his son ... his mind was clearly elsewhere, as he had more important matters to attend to.

Mike won Grammys for Best Rap Album, Best Rap Song and Best Rap Performance -- but today his focus is purely on Mikael's surgery.