Deontay Wilder says his ex-fiancée Telli Swift‘s son’s allegations that the boxer brutally beat him up are totally bogus.

Deontay makes a vehement denial in new legal docs obtained by TMZ … and his legal team goes even further … claiming, among other things, if Kerron Swift suffered any injuries, those were caused by pre-existing conditions or unrelated events.

In addition … they say that Kerron cannot back up his claims of emotional distress, false imprisonment, assault and battery.

TMZ Sports reported earlier … Kerron said Deontay slapped him when he was 13, and in a separate alleged incident, beat him with a belt until he was bruised.

Kerron also claimed Deontay grabbed his throat before throwing him around “like a ragdoll.”