How to make bootbox inside modal dialog?

Question

enter image description here

<div class="modal fade" id="ajax" role="basic" aria-hidden="true">
    <div class="modal-dialog modal-dialog-center">
        <div class="modal-content">
            <div class="modal-body">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal" aria-hidden="true"></button>
                    <h4 class="modal-title">Ajax Content</h4>
                </div>
                <div class="modal-body">
                    <form id="form" class="form-horizontal" role="form">
                        <div class="form-group">
                            <label class="col-md-3 control-label">English：</label>
                            <div class="col-md-8">
                                <input type="text" name="en_key" value="" class="form-control">
                            </div>
                        </div>
                    </form>
                </div>
                <div class="modal-footer">
                    <button type="button" class="btn default" data-dismiss="modal">close</button>
                    <button type="button" class="btn blue" onclick="saveParameter()">Commit</button>
                </div>
            </div>
        </div>
    </div>
</div>



function saveParameter(){
      bootbox.alert({
                  size: "small",
                  message: "Success!",
                });
}

Fist,I show the modal dialog, and click Commit button and alert bootbox, But the bootbox is outside the modal dialog like the picture, How to make bootbox inside modal dialog ??