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!

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.