When viewing a merged pull request, it would be extremely beneficial to list the commit ID associated with the merge commit.

On a page with the URL pattern:

https://bitbucket.org/

{company}

/

{repo}

/pull-request/

{pull-id}

/

{pull-description}

/diff

There is, as best I can tell, no way at all to determine the merge commit associated with the pull request. The only solution is to click the destination repository, then click the branch name, then manually scroll/search through the commit list looking for the pull request.