I think he's a very attractive dog and have no reason to think he's anything but purebred boxer (couldn't really see his body but the long muzzle and the very light color mask are two traits that crop up when you're not consistently breeding for type - the muzzle is a very hard thing to keep, and even the best bred litters can end up with more poor heads than good, and the loss of the mask in a fawn usually happens with multiple generations of fawn to fawn breeding). I don't see any OTHER breed in him, however.
As for having sire and dam on the premesis, it's not an absolute bad sign, but it's something to look for. As Jan pointed out, even in a highly competitive breeding kennel the chances of having the perfect mate for your girl in the same house isn't particularly high, and furthermore, chances are your dogs are already related closely anyway! Most folks I know will keep one male and several girls, but seldom end up breeding them to each other. They have a network of people with dogs related less closely to whom they can turn for breeding close up. Of course there are exceptions, and a breeder might buy a girl from a different line, bring her home and breed her to her male, or lose her old dog and buy back a distant relative and breed her to one of her girls.
There are people who try to buy a quality dog and bitch to breed together, but that's usually putting the cart before the horse, and proving one or the other and then seeking out the ideal mate is preferable.