Katharine McPhee, 23, sure is on cloud nine these days, recently showing off a ring from fiance Nick Cokas, 42, People magazine reports today.

"Katharine is bubbling over with excitement for her upcoming wedding," a source says. "She is all smiles when she talks about the planning. It sounds like everything is going very smoothly."

The couple met in 2005 in a theater production of The Ghost and Mrs. Muir. McPhee and Cokas got engaged in September, and their union began years ago as a friendship, McPhee said.

"He took me up to my San Francisco (American Idol) auditions," she said.

"That's when the relationship blossomed. We totally fell in love."

As for their 19-year age difference, Katharine McPhee says that "was never really a concern" because the two have such a strong connection.

Nick Cokas "just makes things really fun" and "we love business. We love going to meetings together and create things together."

Case in point: the two will join forces on an independent film titled The Last Caller, in which Katharine McPhee will star and Cokas will produce!