Domestic griefs were now embittered by political resentments. Ferdinand valued his daughter mainly as a political emissary; he had formally accredited her as his ambassador at Henry's Court, and she naturally used her influence to maintain the political union between her father and her husband. The arrangement had serious drawbacks; when relations between sovereigns grew strained, their ambassadors could be (p. 176) recalled, but Catherine had to stay. In 1514 Henry was boiling over with indignation at his double betrayal by the Catholic king; and it is not surprising that he vented some of his rage on the wife who was Ferdinand's representative. He reproached her, writes Peter Martyr from Ferdinand's Court, with her father's ill-faith, and taunted her with his own conquests. To this brutality Martyr attributes the premature birth of Catherine's fourth son towards the end of 1514.[499] Henry, in fact, was preparing to cast off, not merely the Spanish alliance, but his Spanish wife. He was negotiating for a joint attack on Castile with Louis XII. and threatening the divorce of Catherine.[500] "It is said," writes a Venetian from Rome in August, 1514, "that the King of England means to repudiate his present wife, the daughter of the King of Spain and his brother's widow, because he is unable to have children by her, and intends to marry a daughter of the French Duke of Bourbon.... He intends to annul his own marriage, and will obtain what he wants from the Pope as France did from Pope Julius II."[501] [Footnote 499: _L. and P._, i., 5718.] [Footnote 500: See above p. 76.] [Footnote 501: _Ven. Cal._, ii., 479. The Pope was really Alexander VI.]