Mallard x Wood Duck hybrid

We saw this interesting duck at the Rhododendron gardens last weekend.

 

Any ideas on what it is???

 

It must be half Mallard and half something else ...

 

My wife thinks it's a Wood Duck cross Gadwall hybrid - the head has the shape of a wood duck's with a bit of a crest (it's hard to see in this photo).

 

Updated: OK, it must be a mallard x wood duck.

Done