Castle season 6 will premiere September 23 on ABC with its first episode titled "Valkyrie."

According to latest spoilers surrounding the upcoming season, actor Joshua Gomez will be guest-starring as a possible murder suspect. Entertainment Weekly reports that the "Chuck" actor will reportedly make an appearance in episode 5 of season 6, as a suspect who claims to have "traveled back in time to stop terrible events from unfolding."

Season 5 ended with Castle's proposal to Beckett, and "Castle" creator Andrew W. Marlowe recently dished to TV guide regarding the intentions behind the proposal.

"He asked his question out of emotion and passion and the circumstances of the moment," he said. "He was challenged to think about what he really wanted in life. His preferred version is that he has this woman in his life."

Marlowe also said, "but he is who he is..," referring to the fact that Castle has been married two times before.

Marlowe also spoke to Give Me My Remote about the proposal. "We're really excited by some of the dramatic opportunities and problems Beckett's answers to the two fundamental questions [raised in the finale] have created. One question is does she accept the proposal? And the other question is she has this job opportunity in Washington D.C. — what's going to happen to that? And I know there's been a lot of attention in the press to how Beckett answers those questions, but what's more interesting to us is that each one of those answers has consequences to their relationship, and to Castle's future and Beckett's future."

Castle is an American crime drama series which follows the lives of novelist Richard Castle (Nathan Fillion) and detective Kate Beckett (Stana Katic) as they solve crimes in New York City. The show not only focuses on solving crimes, but the relationship with Castle and Beckett.