EDMUND AND JASPER TUDOR AND MARGARET BEAUFORT
In 1452, Edmund and Jasper Tudor were formally brought into the royal family and were made earls: Edmund the Earl of Richmond and Jasper the Earl of Pembroke. Their brother Owen was already a monk at Westminster Abbey.
It is not really possible that the two Tudor brothers were looked to as heirs of Henry VI (who had been married to Margaret of Anjou for seven years but still had no children). They had been formally recognized at the half brothers of the King whose uncles -- other possible heirs -- were all dead by this time. But the Tudors had no blood connection to the English throne at this time (although they did to the throne of France through their mother Katherine of Valois).
The new earls were given precedent over all the other nobles of the realm save the dukes and the King and Queen. Along with the titles came estates and revenues, as well as the potential of noble brides.
In March 1453, Edmund and Jasper were given joint custody of Margaret Beaufort, heiress of the Duke of Somerset.
Margaret's grandfather was John Beaufort (d. 1410), who was the eldest son of John of Gaunt Duke of Lancaster and his mistress Katherine Swynford. John later married Katherine and their children from before the marriage were made legitimate by Parliament in 1397. However, Henry IV added the caveat that the Beauforts could never inherit the throne.
Margaret Beaufort was born May 31, 1443. Her father died in 1444, leaving his young daughter a very desirable bride. A few years later, Margaret was married to John de la Pole, the heir of the Marquess of Suffolk. The Marquess himself was murdered in 1450 and in early 1453, the marriage of John and Margaret was annulled.
The annulment may have come at the request of the King, who also may have been the one to match Margaret and Edmund Tudor. The couple were married in 1455.
Edmund Tudor died in November 1456 and his brother Jasper took Margaret the child she was carrying into his protection. The child was a son born in 1457, and was named Henry.
Jasper himself was still not married and wouldn't find a bride for almost 30 years.