The 37-year-old Nicaraguan-born fighter, No. 5 in The Ring's flyweight ratings, has been one of the most exciting fighters in boxing's lower weight categories.

Now though, he has decided to bring the curtain down on his 16-year professional career.

"I think the moment I never expected has arrived," Alvarado (42-5, 25 KOs) told The Ring. "I can no longer compete at the highest level because my body isn't what it used to be years ago. That is why I have decided to retire—primarily for the sake of my health."

Alvarado came up short in his first two world title attempts.

He lost a 12-round decision to Kazuto Ioka in December 2013 for the WBA 108-pound title, before suffering the same fate six months later in Argentina against Juan Carlos Raveco for the flyweight crown.

However, those setbacks strengthened his resolve. He won 14 of his next 15 outings inside the distance to secure an opportunity to contest the vacant IBF 108-pound strap, which he made the most of with a seventh-round stoppage of Randy Petalcorin.

"My happiest moment was October 29, 2018, when I achieved my dream of becoming a world champion in the Philippines," he proudly recalled. "I owe this to my manager, William Ramirez—who believed in me from the very beginning—and my trainer, Luis Cortez."

Alvarado made two successful defenses but like many others worldwide, his career was impacted by the coronavirus pandemic.

He decided on a flyweight move, vacating his title in the process, but was outboxed by then-IBF ruler Sunny Edwards over 12 rounds in November 2022 and stopped in the final round by Masamichi Yabuki on December 31 in his last outing.

"What hurt the most was not achieving a second world title," he explained. "But ultimately, I feel satisfied with everything I accomplished, and I leave with no regrets."

With that in mind, Alvarado isn't leaving boxing completely and intends to remain involved in the sport.

"My dream now is to open my own boxing gym; I enjoy teaching young people," he said.

"Right now, I continue working as a boxing promoter in my country, thanks to the trust placed in me by my manager. We are continuing to work hard, supporting Nicaraguan boxing as I enter this new phase of my life."

Ramirez has known Alvarado from the beginning of the fighter's career, believes their relationship goes beyond the traditional manager-fighter bond and echoes the sentiment they'll continue even in retirement.

"Working with Felix was very easy, he is the most down-to-earth person you can think of, so much so, that when his first contract was up, there was no need to sign another one," said Ramirez, who also managed Ismael Barroso and Cristofer Rosales to world title glory.

"He is a family man, as I am, and I will always be by his side. He started a promotional company in Nicaragua which I have been a part of since the beginning. I'll be right at his side to help with his dreams in anyway that I can."