EF6 Update Foreign Key after insert Data from another Form

I’m trying to update a table’s foreign key after I insert record from a different form.

Table Project:

ProjectID    CommentID

Table Comments:

CommentID   Date    Comment

First, I create the Project and assign CommentID a NULL value since there is no comment yet. So far so good.

Then, in some moment, I need to add a comment to my project. I can successfully add comments, but can’t assign CommentID in related Project table.

This is how I’m trying to do (with no success):

MyEntities ctx = new MyEntities();

tblComents coment = new tblComments()
        {
            Date = DateComent.Value,
            Comment = TxtComment.Text.Trim()
        };

ctx.tblComments.Add(comment);
var projet = new tblProject { tblComments = comment };
ctx.SaveChanges();

Like this, I create the comment but the foreign key is never assigned in table Projects.

Any help?

Thanks

EF6 Update Foreign Key after insert Data from another Form