Missy Franklin 'Disappointed' by Her Olympic Performance

— -- Missy Franklin was one of the breakout stars of the 2012 London Olympics, winning five medals, including four gold.

But Rio has been a different story for the young swimmer, as she failed to qualify for the 200 meter freestyle final -- an upset that left her heartbroken.

"By far, it's been the most disappointed I've ever been in any athletic performance, so for that to line up at the Olympics is not ideal, obviously," Franklin said today on ABC News' "Good Morning America."

"But, you know, that positivity just comes from knowing that I did the best that I possibly could and it just wasn't my week," Franklin said. "It's heartbreaking that all the hard work and sacrifices I made just didn't show up, but I know that they will eventually and I think I'm going to be so much stronger after this experience."

Franklin vows to return to the next Summer Olympics stronger than ever as we look ahead to Tokyo 2020.

"I feel like I have so much left to learn from this sport, so much left to give to it, so I would love to be [in] 2020," she said.

Regardless of her personal disappointments, Franklin said she's proud of Team USA, which dominated this year's Olympics, winning 33 medals including 16 gold.

"It's been so incredible being a part of this journey," she said. "There were so many things that happened this week that were just historic. You know, you look at Michael Phelps, you look at Simone Manuel, you look at Katie Ledecky, so much happened. To just be a part of it and be a part of this incredible legacy we have, it's such an honor."