Rollo's (Clive Standen) betrayal will be felt in the upcoming episode of "Vikings" season 4.

In the promo trailer for the episode titled "What Might Have Been," Ragnar (Travis Fimmel) and his people are heading toward Paris to raid the flourishing city despite the threatening weather. But the real challenge for the Norsemen will be caused by Ragnar's brother Rollo, who is determined to prove his loyalty to his wife Gisla (Morgane Polanski) and her father Emperor Charles (Lothaire Bluteau).

The trailer shows that Rollo will be waiting for his brother's fleet in Frankia, where they will be surrounded by the ships from Paris. Will Rollo's betrayal put an end to Ragnar's quest to conquer Paris?

In addition, the synopsis for the episode states that Ecbert (Linus Roache), the cruel king of Wessex, will send his son Aethelwulf (Moe Dunford) and grandson Alfred (Conor Ó Hanlon) on a trip to Rome. This will feature the start of Alfred's development as the greatest ruler in England.

Meanwhile, History Channel finally announced that the network gave the green light for a 20-episode season 5.

Deadline revealed that the announcement also mentioned that "The Tudors" star Jonathan Rhys Meyers signed on to join the cast of the historical drama series for the upcoming season. However, details about his role are still unrevealed at the moment.

This is not the first time that Meyers will work with the network for a period drama, since he will portray the role of Tom Lea in the upcoming remake of "Roots," set to premiere on May 30.

Meyers could possibly help fill the vacancy in the roster when Standen leaves the show at the end of season 4 after signing on for NBC's new series called "Taken."

The next episode of "Vikings" will air on Thursday, March 24.