The other Prince William is in a long-term relationship with his own version of Catherine

Thirty years ago Valentine's Day, honeymoon baby Prince Guillaume was born to Hereditary Grand Duke Henri and his wife, Maria Teresa of Luxembourg. The other Prince William's parents - Charles and Diana - married in July of that year. The heirs to Luxembourg and the Prince of Wales are very close in age.

And they should get together to talk!

Although both sovereign grandparents are still alive, Elizabeth II still reigns while Grand Duke Jean abdicated ten years ago. William of Wales as heir to the heir can pursue a largely private life while Guillaume takes on a full slate of royal duties.

Romance-wise, Enneagram 9 Hereditary Grand Duke Guillaume of Luxembourg is playing his cards very close to his chest - guess information on his maybe-fiancee will be given out on a need-to-know basis.

That type of discretion would have saved the now Duchess Catherine a lot of sniping.

(Thanks for Marlene Koenig for the info on this interview)
Hereditary Grand Duke Guillaume's 30th birthday interview