It is actually an Air Atlanta ex-Cathay 747-200 (sister to VCAT and VRUM); it will be in Virgin colours with the same fit and IFE as those two aircraft, with Virgin cabin crew.
The reason it's happening is to cover the period while the Virgin classics' interiors are upgraded to the latest standard in an intensive programme early next year. I expect it will also help ease the disruption as the massive effort to get 7 new 744s in service over the next 18 months gets underway!