Teen star Miley Cyrus has vowed to keep her lips locked about her love life, insisting she's "thrown away the key" when quizzed about boyfriend Justin Gaston.

The 15-year-old Hannah Montana star has admitted to dating Gaston, five years her senior, as their relationship has heated up in recent months.

But Cyrus insists she has had enough of the relentless rumours about her love life, since her romance with singer Nick Jonas reportedly sparked a love rivalry with fellow teen star Selena Gomez earlier this year.

When asked about her boyfriend on U.S. TV show Good Morning America, Cyrus hesitates: "Um, I'm going to keep that one zip-tight, locked and throw away the key."