"Their on-and-off-again relationship is currently off," says the source. "But you never know with Miley and Liam. They could be back on at some point."
Miley, who turns 18 on Nov. 23, and Liam, 20, met on the set of "The Last Song" in 2009 and first split in August, then reunited in September.
The singer's parents, Billy Ray and Tish Cyrus, announced their own split last week after 17 years of marriage.