Isabel grew up by the side of her sister-in-law, the young Queen of Scots; and although the latter was four years the senior of her companion, they were close rivals in the learning then becoming fashionable for young ladies of rank. The curious Latin and French didactic letters written by Mary Stuart, aged ten or eleven, to her little sister-in-law, although prim and priggish according to our present ideas, throw a flood of light upon the severe and systematic training for their future position that the young princesses underwent. After making all allowances for inevitable flattery on the part of such a courtier as Brantome, it is evident that Isabel was a beauty of the very first rank. ‘Her visage was lovely and her eyes and hair black, which contrasted with her complexion, and made her so attractive, that I have heard say in Spain that the gentlemen did not dare to look at her, for fear of falling in love with her, and to their own peril making the King jealous. The churchmen also avoided looking at her for fear of temptation; as they did not possess sufficient strength to dominate the flesh on regarding her.’ In 1552 she was betrothed to Edward VI. of England, and this danger to Spain, averted by Edward’s death, made Philip and his father all the more eager to keep a firm hold upon England as soon as Mary’s accession made an alliance possible.
It was this young beauty of fourteen whose portrait by Janet was sent to Philip in the early days of 1559. He was always an admirer of women, and had been twice an affectionate husband; but his first wife he had married when he was but a boy, and she died within a year; and his second wife, Mary Tudor, was, as we have seen, married to him for political reasons alone. Doña Isabel de Osorio, who had been his acknowledged mistress for years, and had borne him children, had retired into a convent, and was, of course, now out of the question. The sight of this radiant young French beauty seems to have stirred Philip’s heart to as much eagerness as he was capable of feeling.[167] But though the bride was an attractive one, and her own family exhausted eulogy in her praise, as well they might, for no princess of her time excelled her, the marriage was regarded on both sides as a political event of the first importance, though, as we shall see, it became really more important even than was anticipated. It was vital for Philip that he should have some control over French policy now that friendship with England was denied him; whilst to have his own clever daughter by the side of Philip was to the King of France a guarantee that no step inimical to him would be taken in Spain without his knowledge, and that he could depend upon the help, or at least the neutrality, of Spain if he had to deal with the French and Scotch reformers, who seemed to threaten the basis of authority. Thenceforward the Catholic sheep were to stand apart from the Protestant goats throughout the world.