7:17 PM PT -- Sources close to Pamela say she stands by Brandon's statement. We're told Pamela left Tommy when their youngest son, Dylan, was just 7 weeks old. For years, Pamela has maintained that the only thing that makes Tommy a "Dad" to Brandon and Dylan is his DNA.

Our sources say Pamela knows her two boys are total gentlemen and the three of them only want the best for Tommy ... they hope he gets help he needs.

Tommy Lee's post honoring his dad on Father's Day got shredded to pieces ... by his own son.

In a clear sign there's plenty of bad blood still left between them, Brandon eviscerated his father with a blistering comment on Tommy's Instagram post honoring his father. Tommy starts by offering sobering thoughts about fatherhood but things went south from there ... with shots at his sons and a parting shot at his ex, Pamela Anderson.

Didn't take long for Brandon to clap back, saying, "Remember what happened last time you said this s***? ... You gotta show up to be a Dad big guy. If you think we're so bad (which I can assure you we are not) then you should have showed up to a few more BDays and baseball games. Someone like you couldn’t raise a man like me. I'm twice the man you'll ever be."

Brandon went on to say, "Once again painting our family in a negative light. Who the f*** are you? Just move on dude ... WE ALL HAVE. Or I'll put you right back to f***in sleep."

Things really escalated because moments after that comment, Brandon posted video on his IG of his father unconscious from the night he punched him, which we're told was in self defense.

As we reported ... Brandon knocked Tommy out cold after a heated argument back in March turned physical. There was a time when it seemed Brandon and Tommy would patch things up. Brandon eluded as much and Tommy said he didn't want his son prosecuted.

So much for that.