This is the beautiful Constance of Castile (1354 – 1394).
She was the daughter of Peter the Cruel (I’m going to start calling my brother that) and Maria de Padilla. Peter and Maria were married in secret- they were forced to have the marriage repudiated, but he still kept her as his mistress. Weird.
Constance married the notorious John of Gaunt, 1st Duke of Lancaster on September 21, 1371. She was his second wife.
As a political power play, Constance entered London with loads of pomp and circumstance as the not-so-official Queen of Castile. She was escorted by Edward the Black Prince and a bunch of other dignitaries. Gaunt wanted a kingdom of his own since Richard II stood in his way from claiming England. This didn’t work. He did not get any crown.
John and Constance had one daughter- Catherine of Lancaster. She became a true Queen of Castile when she married Henry III of Castile (also known as Henry the Sufferer or Henry the Sick).
John married his mistress, Katherine Swynford, after Constance passed away at the age of 40. Katherine, gave birth to four of John’s children while he was still married to Constance. That had to be a fun household.
Constance was the great grandmother of Catherine of Aragon.
More on Constance here: http://womenshistory.about.com/od/medbritishwomen/p/Constance-of-Castile.htm