October 26 in 1538, "Geoffrey Pole, brother of Cardinal Reginald Pole and son of Margaret Pole, Countess of Salisbury, was interrogated in his prison at the Tower of London regarding letters he and his family had received from his brother, and words which he had uttered showing his support for the Cardinal, who had denounced the King and his policies in his treatise, Pro ecclesiasticae unitatis defensione".
The History of Parliament website has more detail about Pole's time in the Tower and the link between his cardinal brother's opposition to Henry VIII's division of the Church and his family's troubles:
It was the raising of his brother to the cardinalate which preluded Pole’s and his family’s downfall. He was the first to lapse into disfavour, perhaps because of his debts. On 1 Feb. 1537 he was warned that John Gostwick, treasurer of the first fruits and tenths, ‘looks for you for the King’s money’, and when Prince Edward was christened in the following October the King refused to receive him at court. In a letter to Chancellor Audley, written from Lordington probably on 5 Apr. 1538, he voiced his distress at the humiliating prospect of visiting London on legal business after Cromwell and others had warned him not to wait upon the King: he may have spared himself, for a week later he joined his fellow justices in examining suspected thieves at Chichester. As late as 9 July he was reappointed to commissions of the peace but at the end of August he was arrested in Sussex and lodged in the Tower: according to Chapuys, he was suspected of having corresponded privately with the cardinal.9
Pole remained in prison for nearly two months, while Cromwell was hearing an improbable story that the cardinal had secretly visited England to confer with his relatives. On 26 Oct. 1538 the first of seven interrogations was conducted by Sir William Fitzwilliam I, Earl of Southampton. Although Southampton was less concerned with Pole’s views than with those of greater figures, two days later John Hussee reported to his master Viscount Lisle that Pole had hurt himself badly in an attempt at suicide, and it was perhaps soon after this, when he was rumoured to be in a frenzy, that Lord Montagu countered his wife’s fears with the reply that it did not matter what a madman said. His kinsmen had indeed but little confidence in him: the cardinal had urged him not to meddle and in the summer of 1538 Montagu had sent to his house to destroy incriminating letters. The government had shrewdly picked on the weakest of its suspects: Pole revealed enough for Montagu and the Marquess of Exeter to be arrested and for a string of confessions to be wrung from their friends and servants.10
By 12 Nov. Pole’s own interrogations were over and his mother’s about to begin. Having thrown himself on the King’s mercy, he was tried at Westminster on 4 Dec. with Sir Edward Neville, a mariner named Hugh Holland, and two priests, John Collins and George Croft. He was accused of having praised the cardinal to Montagu in 1536, of treasonably corresponding with the exile through the seaman Holland, and of declaring that he would make only a formal appearance in arms against the northern rebels. Clearly he would have fled abroad if Holland had agreed to take him, although he denied any intention of joining his brother. The messages he had sent to Reginald included a warning against the King’s plans for assassination and the bleak prediction: ‘The world in England waxeth all crooked, God’s law is turned upsodown, abbeys and churches overthrown ... and I think they will cast down parish churches and all at the last’. All the defendants were found guilty and sentenced to death. The sting of Pole’s confession had lain in the rash statements he attributed to Montagu and Exeter, condemned on the two previous days, and propagandists made play of Montagu’s conviction out of the mouth of his brother. Exeter, Montagu and Neville were beheaded on 9 Jan. 1539, when Chapuys wrote that their accuser had tried to suffocate himself and might escape with life imprisonment: he had in fact been pardoned a week earlier and by April he seems to have been back in Sussex, where his name was included on a muster certificate.11
died shortly before his brother in November 1558 and was buried in the church of Stoughton near Chichester, where his widow also asked to be laid in her will of 12 years later.14
Pole’s royal blood and religious dissidence continued to haunt his children. Two of his sons, Arthur and Edmund, embarked on a futile conspiracy in 1562 and disappeared as prisoners in the Tower, and the second son Thomas inherited Lordington only to die without issue, the manor passing to another brother Geoffrey, a recusant who alienated it before his death in exile.15
There is a modern translation of Reginald Cardinal Pole's open letter to Henry VIII available, with a .pdf here.