EXCLUSIVE: Robbie Amell and Italia Ricci Dish Wedding Details: Stephen Amell's Daughter to be a Flower Girl!

There's going to be an overdose of adorable at Robbie Amell and Italia Ricci's wedding!

Before the engaged actors say, "I do" later this fall, the precious Mavi Amell -- daughter of Robbie's cousin, Arrow star Stephen Amell -- will be walking down the aisle as a flower girl, ET exclusively reveals.

"She's just the most perfect little human," Ricci spilled of the two-year-old cutie and her role in the wedding.

MORE: Stephen Amell's Daddy-Daughter Poolside Photo is Too Precious

ET caught up with the couple earlier this week at the premiere of the highly-anticipated X-Files revival, in which Amell stars as Agent Miller.

When asked how the wedding planning was going, Amell admitted that he wasn't allowed to spill much. "He's not allowed to talk about it!" Ricci joked.

"I got in trouble for releasing the date once," The DUFF star said sheepishly. "But I did just find out she tried on her wedding dress as a joke and she decided to go with it, so I have that to look forward to!"

Sorry, to break the news to you, Robbie -- but we've already known part of that secret! Last year, ET was the first to discover that Ricci actually found her gown while filming season two of the ABC Family drama Chasing Life.

"It's funny because when we were shooting the scene of April trying on wedding dresses," Ricci explained on set in July 2015. "In between takes, we were at a bridal shop, so I was looking around and "I was like, 'This is convenient!'"

"And I found my wedding dress," she smiled. "I bought my wedding dress from the place where April was trying hers on."

WATCH: Italia Ricci Found Her Wedding Dress While Filming 'Chasing Life'!

In addition to their upcoming nuptials, the couple has plenty to celebrate in 2016. ET broke the news that Ricci has been cast as bad gal Silver Banchee for an action-packed arc on CBS's Supergirl, and Amell will also return to The Flash, but this time as the villainous Deathstorm. Talk about a comic book power couple!

When Ricci, 29, and Amell, 27, do tie the knot later this year, they will have been engaged for more than two years. The CW hunk popped the question in 2014 while the duo was vacationing in Big Sur, CA and celebrating six years of dating.

"The only reason we waited was because we wanted the date to fall on two special numbers," the brunette beauty explained of the couple's lengthy engagement.

"I've really just been putting everything off because I'm terrified of all of the decisions." Ricci added, "I want everything."

WATCH: Robbie Amell and the 'Duff' Cast Are Hilarious in These Bloopers!

Despite their busy schedules, the couple is not far behind with the wedding to-do list. Ricci and Amell have locked down a venue in Los Angeles, the menu, and the theme of the day. "[It'll be] classic and elegant -- I mean, I hope," Ricci said with a laugh.

"As classy and elegant as you can get when there are burgers or pizza [being served] -- or maybe both," she added.

The only missing portion of their wedding day details will be to decide which type of flowers Mavi Amell will be spreading during her walk down the aisle. "It's going to be tricky to pick flowers because I don’t like the smell of most of them," Ricci confessed.

No matter which flowers they choose, we have a feeling this will be one of the sweetest celeb weddings of 2016!

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