Duets & Destiny is the series finale of Austin & Ally. It’s the 20th episode of Season 4 and the second part of the two part series finale, as well as the epilogue for the entire series and premiered on January 10, 2016.
Years after the gang has gone their separate ways, Austin, Ally, Trish, and Dez meet-up and learn what they have all been up to, individually.
Austin: Ally, I still love you. I never stopped loving you. I never want to be apart from you.
Ally: I want to be with you, too. But how? No matter how much we love each other, we always seem to be headed in different directions.
Austin: Then why don't we head in the same direction? We can write, record, perform and tour together.
Ally: You mean, like an official duo?
Austin: Yes. What do you say?
- Ross Lynch as Austin Moon
- Laura Marano as Ally Dawson
- Raini Rodriguez as Trish De la Rosa
- Calum Worthy as Dez Wade
- The cast had the table read of this episode on April 13, 2015. 
- This episode began filming on April 16, 2015.
- Despite being the last episode of the series, this episode was the second to last episode filmed.
- In this episode, The Helen Show appears which first appeared in the first episode of the series Rockers & Writers and did not appear again until this episode.
- About the finale, Laura Marano said, "We’re all excited about the projects we have upcoming but it’s like, this is our family, we’ve grown up with each other,” explained Marano. “I mean [the last day was] so emotional— it was really, really sad.” She went to say. “I’m so excited for everyone to see it. I think there was a few surprises that definitely happen, but it’s really, really, great and I think it wraps up really well.”
- In prep for the finale, Disney Channel hosted an Austin & Ally marathon, Austin & Ally Takeover Weekend, a weekend before showing every episode of Austin & Ally.
- This episode is an epilogue, jumping ahead four years, and later, ten years.
- Austin's proposal to Ally shown during the promos turned out to be a joke made by Dez, who was deciding how to end his movie based on Austin and Ally's story. However, Ally told her kids that Austin proposed to her while they were on tour together in Paris.
- Austin marries Ally in the future, Dez marries Carrie and Chuck marries Trish.
- Everyone has kids in the future.
- The final line of the series was said by Ally: " Remember this one?"
- Austin references Rockers & Writers when he tells Ally they have 18 hours to write the greatest song ever.
- In the final scene, Austin and Ally play the melody to the theme song of the show.
- This is the final appearance of Austin Moon, Ally Dawson, Trish De la Rosa and Dez Wade, as well as the last appearances of also Chuck McCoy and Carrie.
- Austin & Ally's final episode drew 3.201 million views, the highest-rated episode of Season 4.
- During the premiere #AustinAndAllyFinale trended and made it to #2 worldwide on Twitter, second only to The Golden Globes on the same night.
- Ally's middle name is finally revealed as Edgar on her Songwriter Of The Year award in the music factory.
- Ironically, Dez & Carrie, who are not that bright at all, had a child who is a genius at age 6.
- The final scene takes place 18 years after Rockers & Writers, in 2029.
- This series officially ends with Austin & Ally getting married in the future, having two kids, and becoming an official duo. Trish marries Chuck and has a kid who's just like her, and Dez marries Carrie and has one kid who is a genius.
- Dez’s shirt says “The End” when he and Carrie visit Ally’s dad’s old music store.