User blog comment:GianG/Merlin characters ages/@comment-5674726-20141116000448/@comment-24492510-20141116193007

Fimber wrote:

 "Gwen's exact words are: "It's been a year since Morgana betrayed him." 

''Meaning "since Morgana betrayed Uther". "The Darkest Hour" is the first episode of season four and Morgana's open betrayal happened in the last episode of season three ("The Coming of Arthur"). A year has 12 months and Gwen says "a year", so a year has passed between season three and season four."''

What I'm trying to say is that Gwen said "it's been a year since Morgana betrayed him", not "it's been a year since Uther understood Morgana betroyed him". Morgana actually betroyed Camelot in the 1st episode of Series Three. In the last episode, Uther only discovered this.

I don't think they lied in the interview... Therefore, Series Three lasted 4 months and Series Four is placed 8 months later (4 months + 8 months = 1 year).