Sir Thomas
... that Sir Thomas, a racehorse purchased by George, Prince of Wales, became the first horse owned by a member of the British Royal Family to win the Derby Stakes?
... that <b id="mwB0I"><a href="./Sir_Thomas_(horse)" id="mwB0M" rel="mw:WikiLink" title="Sir Thomas (horse)">Sir Thomas</a></b>, a racehorse purchased by <a class="mw-redirect" href="./George_IV_of_the_United_Kingdom" id="mwB0Q" rel="mw:WikiLink" title="George IV of the United Kingdom">George, Prince of Wales</a>, became the first horse owned by a member of the <a class="mw-redirect" href="./British_Royal_Family" id="mwB0U" rel="mw:WikiLink" title="British Royal Family">British Royal Family</a> to win the <a href="./Epsom_Derby" id="mwB0Y" rel="mw:WikiLink" title="Epsom Derby">Derby Stakes</a>?