In 1340, at the age of twelve, Joan secretly married Thomas Holland of Upholland, Lancashire, without first gaining the royal consent necessary for couples of their rank. The following winter (1340 or 1341), while Holland was overseas, her family forced her to marry William Montacute, son and heir of the first Earl of Salisbury. Joan later averred that she did not disclose her existing marriage with Thomas Holland because she had been afraid that disclosing it would lead to Thomas's execution for treason upon his return. She may also have become convinced that the earlier marriage was invalid.
Several years later, Thomas Holland returned from the Crusades, having made his fortune and the full story of his relationship with Joan came out. He appealed to the Pope for the return of his wife and confessed the secret marriage to the king. When the Earl of Salisbury discovered that Joan supported Holland’s case, he kept her a prisoner in her own home. In 1349, Pope Clement VI annulled Joan’s marriage to the Earl and sent her back to Thomas Holland, with whom she lived for the next eleven years.