everttrollip

Go to Bitbucket and create a new repository (its better to have an empty repo)
    git clone [email protected]:abc/myforkedrepo.git
    cd myforkedrepo
    
** Make sure you do not create a README **

Now add Github repo as a new remote in Bitbucket called "sync"
    git remote add sync [email protected]:def/originalrepo.git

Verify what are the remotes currently being setup for "myforkedrepo". This following command should show "fetch" and "push" for two remotes i.e. "origin" and "sync"