Beef stew - with left over roast?

[NinjaSlipper]

I have half a cooked beef joint, carrots, onions and spuds (veg uncooked)

I want to make a stew - how do i keep the beef tender as its already cooked?

Haven't really done it before

I think I'd put it in near to the end as long as it is tender. Alternatively, I would consider a pie.