long–lost 
/ˈlɑ:ŋˈlɑ:st/ adjective
always used before a noun /ˈlɑ:ŋˈlɑ:st/ adjective : lost a long time ago : not seen or found for many years
▪ a long-lost masterpiece that has recently been rediscovered ▪ He embraced his old friend like a long-lost brother.
▪ a long-lost masterpiece that has recently been rediscovered ▪ He embraced his old friend like a long-lost brother.
