How to display linq IGroup result to gridview

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LINQ

I have a linq query,

var j=from o in Orders
       join  OT in OrderDetails on o.OrderId equals OT.OrderId
       group OT.ProductId by o.OrderId into g
      select new{OrderId=g.Key,ProductId=g};

j.Dump();

It returns the data as,

5IOrderedQueryable<> (4 items)4
OrderId ProductId
13 Key= 13
5IGrouping<Int32,Int32> (2 items)4
32
40

14 Key= 14
5IGrouping<Int32,Int32> (3 items)4
39
48
49

15 Key= 15
5IGrouping<Int32,Int32> (2 items)4
43
30

16 Key= 16
5IGrouping<Int32,Int32> (3 items)4
43
48
49

---
I binded this query to gridview as ,

var j = (from o in con.Orders
        join OT in con.OrderDetails on o.OrderId equals OT.OrderId
        group OT.ProductId by o.OrderId into g

         select new { OrderId = g.Key, ProductId = g }).ToList();
gridview.DataSource = j;
gridview.DataBind();

like this, but whe i execute i got gridview displaying like this,

Order Id Product Id
13 System.Data.Entity.Core.Objects.ELinq.InitializerMetadata+Grouping`2[System.Int32,System.Int32]
14 System.Data.Entity.Core.Objects.ELinq.InitializerMetadata+Grouping`2[System.Int32,System.Int32]
15 System.Data.Entity.Core.Objects.ELinq.InitializerMetadata+Grouping`2[System.Int32,System.Int32]
16 System.Data.Entity.Core.Objects.ELinq.InitializerMetadata+Grouping`2[System.Int32,System.Int32]

how to make gridview to display like this i want,

OrderId ProductId
13 32
40
14 39
48
49
15 43
30
16 43
48
49
like this , pls help me