Del Rio was the Jaguars' head coach from 2003-11, and coming off an 8-8 campaign in 2010, he was blindsided by the pick.
"I had no idea we were going to draft Blaine Gabbert. No idea," Del Rio told ESPN Jacksonville 690 on Tuesday.
The Jaguars had the No. 16 overall selection that year before dealing it and a second-round selection to move up to No. 10 overall.
"In fact, I left to go get something to eat because our pick wasn't for much longer in the draft. I'm sitting there filling my plate thinking, 'Oh great, we've got a couple more hours before we pick' .... and I see, 'The Jaguars are on the clock.' And I'm like, 'What the blank is going on?'" Del Rio said.
Upon walking back into the draft room, Del Rio said he could read on people's faces that they knew it had been "wrong" to leave him out of the process.
"My son and I had ranked all the quarterbacks and we liked Blaine," Del Rio said. "... We liked him, he was in the Nick Foles range - like third, fourth round. He wasn't a first rounder, he wasn't a guy to trade your draft and go up to get him at No. (10). So that was not part of coaching, that was not part of me. That was my first indication that my time in J'Ville was running short."
Del Rio said he had hoped to save that tidbit for a book some day.
However, he was not forced to play Gabbert in his rookie year. The Jaguars went 5-11 in 2011 and Del Rio was fired after Week 12.
Gabbert lasted just three years in Jacksonville, where he went 5-22 as a starter.