"The story of Liam Hemsworth and January Jones is entirely fabricated by US Weekly. There is no truth whatsoever to this tabloid fiction," Hemsworth's rep said.
Hemsworth, 23, and Jones, 35, were first linked this spring after the pair were spotted leaving an Oscars party together, around the same time Cyrus was spotted without her engagement ring.
And more recently, sources close to the couple say Hemsworth is "just weeks from calling [their engagement] off permanently." They said he found Cyrus's raunchy performance at the MTV Video Awards "mortifying" and "he is over her."
The pair were last seen in public together at the Los Angeles premiere of Hemsworth's latest film, thriller "Paranoia."