Do you know what kind of duck this is?

My Mom runs an animal refuge. Has for over 20 years or so. She takes in mostly animals that can't be taken to the local animal shelters, ducks, turkeys, chickens, and more. I swear if someone had a homeless elephant she'd probably say yes!
I'd ask you all to like her FB page but I don't know if that's allowed here so I'll skip it.
Recently a woman called and needed a place for her "mallard" duck, she was moving and didn't want to just leave it behind.
Of course my mom said yes, she'd take it.
Well she brought it out and it's not a mallard. My mom sis etc are all curious.
I said, I'll go on BYC and ask them!! and here I am

Any Ideas what he could be?

 

I'd say he's about the size of a Rouen or a bit smaller, but definately much larger than a Mallard. He's currently in a pen with 4 foot fencing so I'm going to guess he can't fly?
I'm not sure if he's a purebred or not. She said, she bought/got some ducks - let em loose to be on the near by pond. He was the only one left when she was going to move. She didn't even know if he was a boy or a girl. After the initial phone call, she called again to see how to catch him. We're just glad she did the responsible thing and didn't just leave him there!
Now you guys know as much as we do
If he's mixed, which of course is possible - what do you think he may be?
It'd kinda be cool to know, even if it's a good guess .

 

I was on the internet this morning and ran across a picture of a male Welsh Harlequin duck that looks exactly like him.
Could this be what he is? It is technically a mix breed duck from what I read they were originally a Khaki Campbell reject color til a Welsh farmer decided it was a good look and bred them to be this color....