Pepsi has Beyonce and Sofia Vergara, and now Coke has Taylor Swift.

The 23-year-old singer will partner with Diet Coke on a series of branding initiatives, Ad Age has learned. It's not clear how Diet Coke will use Ms. Swift, though it's likely she will become a brand ambassador of sorts, with the partnership going beyond simply 30-second TV spots. However, executives close to the company noted she will not be involved in the company's Super Bowl campaign. A Coca-Cola spokeswoman declined to comment.

Ms. Swift doesn't have the superstar presence of the leotard-wearing, vigorously-dancing Beyonce, who was named the official brand ambassador of Pepsi last month. In addition to being one half of entertainment's highest-wattage power couple along with Jay-Z, Beyonce is headlining the Super Bowl halftime show sponsored by Pepsi, performed at Barack Obama's second inauguration, has starred in movies and will be the subject of autobiographical HBO documentary next month.

Still, Ms. Swift's power is rising fast. According to Billboard's list of 2012's top 40 Money Makers, the star blew past competition like Adele and Lady Gaga to come in at No. 1, with earnings of more than $35 million last year. Her newly struck deal to rep Diet Coke follows a lucrative contract with Cover Girl, as well as work for Sony Electronics and Keds. She's been nominated for 15 Grammy Awards and taken home six. And there's no denying too that she's a favorite of celebrity magazines; the paparazzi love to document her short-lived romances, which include everyone from singer John Mayer and One Direction's Harry Styles to actor Jake Gyllenhaal and Conor Kennedy, son of Robert Kennedy Jr.

While various celebrity endorsements of the soda giants have been ridiculed over the years as less than authentic -- a decade ago Britney Spears was photographed drinking Coke while under contract with Pepsi --"Red" artist Ms. Swift may actually be a genuine fan of Diet Coke.

In October she rather comically told Bon Appetit magazine the cola is always in her refrigerator, "because it understands me." She was also photographed clutching a can of Diet Coke in London earlier this week.

The partnership comes as Coca-Cola has quietly handed a marketing project to Droga5, Ad Age has learned. The New York-based indie has rapidly been gaining prominence on the beverage giant's roster at the expense of other longtime agencies.

The Diet Coke work Droga5 snagged comes just months after it was named creative agency of record for Coke Zero in North America.

However, Wieden & Kennedy remains Diet Coke's agency of record, said Susan Stribling, a Coca-Cola spokeswoman, noting the agency's work around the recently launched "Heart Truth" campaign.

"It's not unusual for us to occasionally tap into more than one agency for a big core brand like Diet Coke," Ms. Stribling said. She said the partnership is a 2013 effort, so it's yet unclear how much the agency will be working with Ms. Swift.

In August, Droga5 replaced Coke Zero's agency of seven years, MDC Partners' CP&B. It's first work for that brand is expected to launch around NCAA Basketball March Madness. It's believed the agency moves were led by Pio Schunker, head of integrated marketing at Coca-Cola North America.

Since 2010, when Diet Coke inched past Pepsi to become the No. 2 soda in the country, the brand has sought to push its advantage in North America, ramping up marketing throughout the year. Last year Diet Coke also made a permanent change to its packaging for the first time in more than five years.