Lady Jane Grey. She was actually fifth in line to the throne but was his personal choice as she was a Protestant. She was only 16 or 17 years old.
More importantly before his passing Edward had determined that Jane was to be his heir though. Jane Greys grandmother was Mary Tudor Queen of France and younger sister of. Eventually Northumberland explained that the king had died.
But her life is far from a tragedy.
She was a viable heir to the English throne because of her maternal grandmother Princess Mary Tudor. Two of his sons would follow him to the block. Through her mother Lady Frances Brandon she was the great-granddaughter of Henry VII. Once the executioner had had time to make his way back from Tower Hill Jane was led out to the scaffold.