pure...??

It doesnt look like belgian coat to me..... the color is off, the saddle is too pronounced.  The coat length is short for a belgian and the ruff is minimal.  There are very few furnishings (front leg feathers) or britches (rear leg feathers).  All the attributes in the many pictures say GSD or GSD mix to me.... As does the lack of masking on the head.

 http://www.bigmtnbelgians.com/

 Here are some shots that show the differences in furnishing and britches

jehanii

he is unpedigreed and ya.....he has five fingers in the rear claws.

 I have never seen a GSD with five toes in the rear......even if the OP meant four toes and a dew claw.....never ever seen that.

Liesje

I'm with Dum, it does look like a "king" shepherd.

You're right! I'm jumping on this bandwagon. It is a King GSD, I believe. I have never seen one before. 

http://www.dogbreedinfo.com/kingshepherd.htm 

American dog breeders Shelley Watts-Cross and David Turkheimer developed this large breed from American and European German Shepherd Dogs, Alaskan Malamutes, and Great Pyrenees.

That's where the fluffy coat comes from.  

Oooh, I didn't see the full body pics at first. I agree, King Shepherd.

dont forget the Shiloh Shepherd

http://www.dogbreedinfo.com/shilohshepherd.htm 

Both the King Shepherd and the Shiloh Shepherd weigh 100-130 or more lbs. The OP states that his dog weighs 37-40 kg, which is 81-88 lbs...

I'm not so sure anymore.  

Since a lot of kings and shilohs are just poorly bred GSDs with some random outcrossing, I think the OPs dog is a GSD with bad structure (as far as the standard) or someone's attempt at a king. 

 well he sure is handsome and regal - I am not - at all -  an expert on GSD's but I believe you have said  you are in Pakistan perhaps it is a cross with one of the Eastern breeds  (I am not up on these breeds but thinking of some of the Tibetan breeds or shepherds ) 

I'd say GSD or mix.  I would hesitate to say King Shepherd simply because I'm not sure if they're bred in other countries

Well, from what I've read on this forum, people (not here, in general) wouldn't know a purebred if it bit them in the a**!  So, who cares if he is or not, and if you want, you could say "yes, he's a purebred longhaired GS"!  Nobody would know the difference.  He's a beautiful dog, I've seen your other post w/ his pics and he's beautiful.

I would say ask "fouriscompany", since she has 2 dogs very similar, but she thought it was a mix.  I'm not contradicting that, since I have no freakin' idea!  I would have said "yes", so...that's my dumbfounded opinion.  LOL