如图，$\mathit{\Delta ABC}$、$\mathit{\Delta BDE}$都是等腰直角三角形，$\mathit{BA}=\mathit{BC}$，$\mathit{BD}=\mathit{BE}$，$\mathit{AC}=4$，$\mathit{DE}=2\sqrt{2}$．将$\mathit{\Delta BDE}$绕点$B$逆时针方向旋转后得△$\mathit{BD}\text{'}E\text{'}$，当点$E\text{'}$恰好落在线段$\mathit{AD}\text{'}$上时，则$\mathit{CE}\text{'}=$　　．