Complex sentence: He testified for the defense during Mulder's murder trial in "The Truth" where he revealed that Teena Mulder had an affair with CSM, and that he and Fox Mulder are half-brothers.
Split into simpler sentences: He testified for the defense during Mulder's murder trial in "The Truth". He also revealed during the trial that Teena Mulder was having an affair with CSM, and that he and Fox Mulder are half-brothers.