A source tells ET that the pair, who got engaged back in February, "have begun planning their wedding" and are "having so much fun with all the details."
"They are both so busy that they now set aside down time to plan all the personal details," the source says. "They are both on the same page about making their wedding a little different. They want it to be modern and exciting."
One of those differences, the source says, may be linked to a focal point of the wedding -- Perry's dress.
"She is leaning away from wearing white and her family is doing their best to encourage her to be more low-key, but that doesn’t seem to be her," the source says. "This is Katy and Orlando’s day and they are going to create a special moment that best represents their style, which means a beautiful celebration of their love with the people they most care about."
"They are so ready to start their new life together," the source adds. "Their plan is to have a close friends and family wedding in the fall, but are keeping many of their plans private."
One unexpected person who may be present for the big day is Taylor Swift, with whom Perry recently reconciled after a years-long feud.
"They’ve already talked guest list, and have even talked about including Taylor Swift!" the source claims.
Swift and Perry's long-awaited makeup came with Perry's cameo in her former foe's video for "You Need to Calm Down," which dropped earlier this month.
"When we saw each other, it was just very clear to both of us that everything was different, that we had grown up, and that we had grown past allowing ourselves to be pitted against each other, and it just was very, very clear that we remembered how much we had in common," Swift explained. "So, both of us have been in a really good place for a while, but I don't think either of us really knew if we were ever going to talk about it publicly."
A source previously told ET that Perry agreed to appear in Swift's music video due to the strong messaging in support of LGBTQ equality.
"Katy agreed to do the music video because both she and Taylor are on the same page in regard to LGBTQ rights," the source said. "They have both been big activists and feel very passionately about the cause. The video features RuPaul‘s Drag Race queens and many LGBTQ icons. That is why Katy agreed to do the video and put their issues behind them, because she felt it was for a good cause that she cares about."