"Promised" is the fifth episode of the fourth season of Vikings. It is the thirty-fourth episode of the series overall. It first aired on March 17, 2016. It was written by creator Michael Hirst and directed by Helen Shaver.
There's an air of betrayal as those whom Odo trusts plot against him; Ecbert agrees to support Kwenthrith in Mercia; Pregnancy brings happiness to Lagertha and Kalf and a marriage is arranged.
Ragnar and Bjorn discuss whether or not they trust King Harald, parenting, and being husbands, while Ragnar claims he's failed at both. Ragnar appears addicted to Yidu's "medicine", and the two discuss their deepest secrets. Yidu's father is a Chinese Emperor, while Ragnar reveals the slaughter of his England settlement, and that he has lost the desire to explore distant lands. King Harald's brother, Halfdan the Black, arrives in Kattegat and lets Ragnar know he is eager to raid and kill Christians. Meanwhile, Torvi reveals to Bjorn that the ring he's carrying, which he took from the Berserker, is Erlendurs. In Wessex, Aethelwulf and Judith argue over both of their wrong doings, and Judith tells him that they are husband and wife only in name. Aethelwulf agrees with Queen Kwenthrith, and tell his father and King Aelle they need to fight together and restore Kwenthrith's power in Mercia. In Paris, Therese and Roland reveal to Charles that Odo plans to overthrow him. In Hedeby, Lagertha reveals to Kalf she is pregnant, and Kalf asks her to marry him. Moments before their wedding, Lagertha stabs and kills Kalf, reclaiming her status as Earl Ingstad, ruler of Hedeby.
- Travis Fimmel as King Ragnar
- Katheryn Winnick as Lagertha/Earl Ingstad
- Clive Standen as Duke Rollo
- Gustaf Skarsgård as Floki
- Alexander Ludwig as Bjorn
- Alyssa Sutherland as Queen Aslaug
- Ben Robson as Earl Kalf
- Lothaire Bluteau as Emperor Charles
- Peter Franzén as King Harald "Finehair"
- Jasper Pääkkönen as Halfdan "The Black"
- Linus Roache as King Ecbert
- Amy Bailey as Queen Kwenthrith
- Dianne Doan as Yidu
- Moe Dunford as Prince Aethelwulf
- Maude Hirst as Helga
- Ivan Kaye as King Aelle
- Owen Roe as Count Odo
- Edvin Endre as Erlendur
- Georgia Hirst as Torvi
- Jennie Jacques as Princess Judith
- Seán T. Ó Meallaigh as Prudentius
- Morgane Polanski as Princess Gisla
Additional Cast (in order of appearance)
- Des Carney as Waerferth the Scout
- Conor O'Hanlon as Alfred
- Huw Parmenter as Roland
- Karen Hassan as Therese
- Philip O'Sullivan as Bishop Edmund
- Stephen Rockett as Hvitserk
- Luke Shanahan as Ubbe
- James Quinn Markey as Ivar
- Elijah O'Sullivan as Sigurd
- Maxim Boshell as Ivar's Axe Boy
- Unknown Baby Actor as Aethelred