"They've actually been engaged since March but kept it a secret," a source told Us Weekly in the magazine's October 15 issue. "Her family wants Katharine to focus on her career and not get sidetracked."
Cokas, a 42-year-old actor, reportedly proposed marriage to the 23-year-old McPhee with a pink and yellow engagement ring last spring.
"The ring is really beautiful," the source told Us. "Only her closest friends have seen it."
Despite the fact the couple has been dating for more than two years, the source told Us that Cokas has spent the last several months trying to win over McPhee's family.
"Nick has worked really hard to build a relationship with her family," the source told Us.
McPhee's representative could neither confirm nor deny that the Idol 5 runner-up is engaged to Cokas.
"We don't comment on our artists' personal lives," the representative told Us.
While there may be some uncertainty about her personal life, McPhee's professional career seems to focused more on acting than music right now -- she's currently involved with three films, the comedy I Know What Boys Like as well as independent films The Last Caller and Success.