Simplify the following text for a Grade 4 native English-speaking person.
Original: The Stargate SG-1 seventh season ended in a two parter episode , `` Lost City '' , was supposed to be a bridge between Stargate SG-1 and the new spin-off , either a show or a movie , which was not planned to run at the same time as Stargate SG-1 .
Simplified: It is a spin-off of the Stargate SG-1 series .