James Muriel and Sarah Darling
11/14/2013 at 02:00 PM EST
Since accepting her English boyfriend's proposal in mid-April during a romantic getaway to Key West, Fla., Sarah Darling has been bursting with happiness – and a sweet secret.
The country singer and graphic designer James Muriel actually went directly from "Will you?" and "Yes!" to "I do" in an intimate ceremony on the beach that very weekend, she reveals to PEOPLE Country exclusively.
"We had dated long-distance for more than a year, so when he moved to Nashville we knew right away we wanted to be together as husband and wife," she explains.
"We just decided very spontaneously to get married. Saying our vows beside the Atlantic had special meaning because it was what separated us, and now we came together beside it."
The guest list was limited to immediate family, so rather than hurt those not included, the couple decided to keep the marriage to themselves. However, "it's hard to keep something like this secret when you are as happy when we are," Darling, 31, says.
The proposal-to-wedding was so blink-of-an-eye that Muriel, 30, lacked an engagement ring for his love. He is designing one now and expects to put the bling on her finger before a formal ceremony the couple will host May 30 in Nashville.
"Our wedding in Key West was perfect, but taking our vows in front of everyone we love will be even more special," Darling, who is working with designer Jim Hjelm on her big day dress, tells PEOPLE.
For more details of Darling's wedding, as well as Kelly Clarkson, Ashley Monroe and Tom Gossin's nuptials, pick up the new issue of PEOPLE Country, on newsstands Friday.