De Vere was a close friend of Richard II as well as being part of the extended family. He was married to Philippa de Courcy, whose mother was Edward III’s eldest daughter Isabella of Woodstock. He was such a good friend that Richard made him a duke – he was the first non-royal to be granted the title which probably didn’t go down terribly well with Richard’s relations.
During the mid 1380’s de Vere decided that he no longer wished to be married to Philippa, preferring instead to marry his mistress who was one of Anne of Bohemia’s waiting women. When the couple married in 1376 Philippa was under ten years old so when de Vere took up with his mistress and caused a national scandal she was still a young woman. Agnes Lancecrona may have been Czech and although she was one of the queen’s domicellas she had no family in England, no land, no money and no political clout. Monastic chroniclers described her as low born and ugly – they said much the same of Edward III’s mistress, Alice Perrers.
De Vere managed to persuade the Pope to annul his marriage and then it was a case of marrying his mistress and living happily ever after. The only down side to this scenario is that Agnes appears to have been abducted on the orders of the earl who appears not to have taken no for an answer, although equally given that he was a friend of Richard II it’s equally likely that the records were blackened by those wishing to vilify the earl and further discredit Richard II. Armed retainers carried Agnes to Chester where there seems to have been some form of marriage. That winter de Vere lost the Battle of Radcoat Bridge and fled the country. Agnes may have gone with him because there is no further reference to her.
As for Philippa, her mother-in-law, Maud de Ufford (a descendent of Henry III) backed her and in 1389 the annulment was reversed. De Vere never returned to England. He died in 1392 but Philippa was granted an annuity as well as her dower rights. And the Czechs, since we’re on the subject, got the blame for quite a lot aside from adulterous earls…apparently the fashionable pointy shoes of the period were entirely their fault.