Portrait of <a href="https://en.wikipedia.org/wiki/Robert_Cecil,_1st_Viscount_Cecil_of_Chelwood" class="extiw" title="w:Robert Cecil, 1st Viscount Cecil of Chelwood">Robert Cecil, 1st Viscount Cecil of Chelwood</a> (1864-1958)
<bdi><a href="//commons.wikimedia.org/wiki/Category:20th-century_unidentified_photographers" title="Category:20th-century unidentified photographers">Unidentified photographer</a>
</bdi>
no later than 1922
The World's Work, 1922: <a rel="nofollow" class="external free" href="https://archive.org/stream/worldswork43gard#page/306/mode/2up">https://archive.org/stream/worldswork43gard#page/306/mode/2up</a>