"I'm happy for Eli, because I know he's at peace and he put a lot of time and thought into this decision. But I am sad, because I won't get to see him play anymore," Peyton said in an interview with Aric DiLalla of DenverBroncos.com.
"And after my dad and Dan Marino, Eli really was my favorite player. So I have to find a new one. But for really 19 years going back to his three years at Ole Miss, 16 years in the NFL, I have enjoyed watching him play, watching him compete, watching him grow into a man. It's been a heck of a run."
Since retiring in 2015, Peyton has been a regular at his younger brother's games, including Eli's final game, a Week 15 win over the Miami Dolphins.
"I really have enjoyed watching him play in person a lot more," Peyton added. "I've been averaging about three games a season during the years that I was retired. I certainly got to keep up with his games more.
"... But to go see him play and take my kids down to the locker room and have the chance for them to see their uncle, that was a real thrill. So I'll miss that."
The brothers each won two Super Bowls during their lengthy careers.
Eli will hold his retirement press conference Friday at 11 a.m. ET.