'Doctor Who' favourite River Song may be written out in the next series.The beloved recurring character - played by 'E.R.' actress Alex Kingston - could be about to depart the BBC sci-fi series for good after a set worker spotted a tombstone prop with her name on it, according to the Daily Star newspaper. The source said: ''There is a River Song tombstone. This is an actual prop.'' The character was first introduced by current showrunner Steven Moffat during Series 4 in two-part adventure 'Silence in the Library'/'Forest of the Dead'. River appeared opposite Tenth Doctor David Tennant as someone of great importance to the Time Lord but it was the first time he had met her as their time lines were moving in opposite directions. The character actually died in the adventure. River then became a larger focus of the show in Series 5 when Steven took over as executive producer from Russell T. Davies and Matt Smith joined the show as the new Time Lord. The feisty space traveller - whose real name is Melody Pond - was later revealed to be the daughter of the Doctor's recently departed companions, Amy Pond (Karen Gillan) and Rory Williams (Arthur Darvill). River also had to marry the Doctor in the Series 6 finale in order to save the universe. The Doctor's long-time foes The Cybermen have also been confirmed to be making a return as well as classic monsters the Ice Warriors. The second half of Series 7 of 'Doctor Who' - which stars Jenna-Louise Coleman as new companion Clara - begins on March 30.