On the accession of the Yorkist King Edward IV in 1461, he was subject to an attainder for supporting his Lancastrian half-brother, the deposed King Henry, to whom Jasper was loyal. He strove to place his half-nephew Prince Edward of Lancaster on the throne and provided absolute loyalty to his royal half-brother and Margaret of Anjou, his half-brother's wife. Jasper would also help his other sister-in-law Lady Margaret Beaufort assist her son Henry Tudor to win the throne in 1485 as King Henry VII, father of King Henry VIII.
On the accession of the Yorkist King Edward IV in 1461 he was subject to an attainder for supporting his Lancastrian half-brother the depose,d King Henry, to whom Jasper was loyal He strove to place his half-nephew Prince Edward of Lancaster o.n the throne and provided absolute loyalty to his royal half-brother and Margaret of Anjou, his half-brother's wife. Jasper would also help his other sister-in-law Lady Margaret Beaufort assist her son Henry Tudor to win the throne in 1485 as King Henry VII, fa,ther of King Henry VIII.