The rapid creation of Reese's Pieces Peanut Butter Cups, a mashup of two well-known treats, is a case study in how brands can more quickly come up with new items and engage with fans.

In case you missed it, Reese's Cups and Reese's Pieces are getting together this summer. As the product won't hit stores until July, Hershey Co. was not exactly ready to announce it as early as it did, with an official confirmation on May 12 after a week of teasing.

Marketers often work slowly and methodically, analyzing every last detail and going through consumer testing before a product gets the green light. In this case, the product is going from idea to market in roughly eight months.

Here's a look at how Reese's went from idea to action.

After meeting with agencies Arnold Worldwide and Havas to discuss Reese's brand equity and campaigns five or six months ago, the Reese's team hopped on a train to head back to Hershey, Pa.

"A bunch of us on the brand team on a train back from New York [were] brainstorming and we were like 'what if you put Reese's Pieces inside of Reese's cups?' And we were like 'Oh my gosh, that's it. That would be the ultimate Reese's experience,'" recalled Ryan Riess, senior brand manager on the Reese's brand. "It would be an equity explosion."

Mr. Riess admits the team did not start from a consumer need state as it normally would, and stressed that the usual route is still the right way to go about innovation "in most cases."

The excitement on the train was so palpable that even before the ride ended, Mr. Riess emailed someone in research and development to see if such a product was even going to be feasible. He did not get no for an answer.

"On the train we had our first hint that maybe this was possible," Mr. Riess said. "By a week later we had already contacted the Reese's plant here in Hershey and had scheduled a trial run and put together the logistics of what needed to happen to make it happen."

Within six weeks, Reese's was running the actual product on the line at the plant, recalled Amy Minderman, senior associate brand manager, Reese's.

A few months later Hershey began telling some retailers about the product's summer debut. The company planned to make a splash with the concoction at the National Confectioners Association's Sweets and Snacks Expo, an annual trade show scheduled for May 24-26 in Chicago. That plan was scrapped after a late April post about the possibility of the candy caught on.

The brand had not planned to discuss the product with the broader public until August or September, once stores already had it in stock. But it wanted to respond to fans who were wondering on social media whether it was real, and hoping it was. While the product is real, Mr. Riess said the final packaging will be different than what was posted.

An internal and external team came up with teasers. The effort first centered around two celebratory days. On Cinco de Mayo, it posted about fake Reese's Pinata Cups.

A later post referred to Mother's Day.

The brand posts included the hashtag #Cupfusion, allowing Reese's to first use word play on consumers' confusion and later the fusion of the two products.

Internally, those working on the project included the Reese' brand team, corporate communications, the digital group, the H-pulse social team and design. External partners include Soulsight, Ketchum, Havas and UM.

Originally, Reese's planned to drag out #Cupfusion until May 21, leading into the trade show. Instead, Reese's held a Facebook "press conference" to officially reveal the product and issued a press release on May 12.

Reese's had already been working on its brand voice and interaction in recent months. For example, it won a Webby award -- and had some fun -- by engaging with people's responses to its Reese's trees, which in a lot of cases did not really resemble Christmas trees.

"The brand is always on, the consumer owns the conversation, and you kind of have to respect what the consumer wants to hear and wants to talk about," Mr. Riess said.

The product idea has clearly caught on in Hershey, where Mr. Riess joked he needs a security guard posted at Ms. Minderman's desk, since she has the samples. Someone who knows Mr. Riess works on the Reese's brand stopped him at Hershey Park over the weekend to ask for some.

Even though the product is still not available (expect lines for samples at the trade show, candy fans), Reese's now posts on social media with a "Cupmoji" character of a cup with eyes made of pieces and a little smirk.

Over the next two months, Reese's might suggest DIY ideas on Pinterest or use other ideas to keep the product in people's minds, and then make a bigger splash in August and September. The mashup cups will not be the only thing the brand talks about for the next few weeks.

On Monday, Reese's said it had not reached out to Marlena Courchain, known as @candyhunter on Instagram, whose post made #Cupfusion a reality -- yet.