"It's weird and sucks that I robbed you," Mack writes to Lamar via text message.
The rapper, a newcomer himself, ironically completed the feat with an album called The Heist, which he and producer Ryan Lewis delivered independently.
"You got robbed," Mack wrote via a text message to Lamar after the show. "It's weird and sucks that I robbed you. I was gonna say that during the speech. Then the music started playing during my speech, and I froze. Anyway, you know what it is. Congrats on this year and your music. Appreciate you as an artist and as a friend. Much love."
Mack posted a screen shot of the text to his Instagram, reports HipHopDX.
Elsewhere online, both he and Lamar were Twitter trending topics during the broadcast, and actor Michael Rapaport (longtime hip hop head and co-star of genre cult classic Higher Learning) refused to hold back when he weighed in.
"Macklemore won best Rap record at the Grammys.OMGOODness.hiphop is dead & KILL the d--n Grammys.where the hell is RAKIM?Macklemore ain't Rap," Rapaport wrote, according to Complex.com.
"... RAKIM,KRS1 & BDK are shaking there d--n heads to break beat Over the fact that Macklemore won best Rap album at the bulls--t a-- Grammys," he added [note for the non-believers: "BDK" is Big Daddy Kane].
Prior to winning the award, Macklemore predicted that it would be a travesty if he won, and news leaked that the Grammy committee debated whether or not Mack and his DJ partner are even hip hop enough.
Ultimately, however, Macklemore and Ryan Lewis ended up with four wins total — also including Best New Artist and Best Rap Performance and Best Rap Song for "Thrift Shop" — and helped to make television history when, during their performance (of "Same Love"), 33 same sex and straight couples were married in a mass ceremony officiated by Queen Latifah.
Lamar, nominated seven times, lost in every category. "You know he raps and people receive it as that, it's just opinions," Lamar told MTV News on the pre-show red carpet about Macklemore. "He just needs to do him. I wouldn't listen to what nobody got to say."
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(Photos from left: Frazer Harrison/Getty Images, Christopher Polk/Getty Images)