We have the same thing with Bob- she looks to be a similar build to him.
We don't really notice it until I see him next to a dog I used to think was big, like a Lab. But when we are out with him people invariably stop us and say how big he is.... followed by can they have him. (Jon says yes and I say no)
I'm looking forward to seeing the pair of them together.
Sometimes I just look at Bob and Bren as they are hurtling along off lead and just revel in the transformation in them. Bob was always content, as long as you love him, but Bren has become a happy, lively pup who just loves life.
I can't imagine having any other breed of dog now