Gosh

Upon seeing the Doctor's TARDIS had landed in the Diaz Household garden, Star Butterfly shouted "Oh my gosh!", moments before the Doctor flew the TARDIS away again. (TV: Untitled)

Behind the scenes
The phrase "OMG" can be used to mean "Oh my god", "Oh my gosh", or "Oh my goodness". In its uses by Jonathan Ross and Supergirl in The Doctor Drops In and Supergirl Meets E.T., respectively, it was not made clear which meaning the characters were using.