He returned to England after the death of the Lord Protector Oliver Cromwell and was a suspect member of a group of Cavalier agitators in the Bristol area.
Gerard was released without charge, but John was tried for high treason, was found guilty of plotting to assassinate the Lord Protector Oliver Cromwell and was executed in May of that year.
[2] Between 1673 and 1680 (while the Exclusion Bill agitation was maturing) it was asserted by the country party that Charles II had legally married Lucy Walter—his mistress while exiled on the European Continent in the late 1640s and early 1650s, and the mother of his son the James, Duke of Monmouth.
[5] It was believed in course of time that the contract of marriage was preserved in a black box in the possession of Sir Gilbert, who was son-in-law of Bishop John Cosin (died 1672), a confidant of Lucy Walter.
In a novel which had a wide circulation it was the designing Prince of Purdino (James) who advised his brother, King Conradus of Otenia, to marry the beautiful "Lucilious", but, in order to avoid disgusting the Otenians, to do so with the greatest privacy imaginable, and in the presence of but two witnesses, himself and the priest (Cosin).
Gilbert married first, Mary, daughter and heiress of Charles Berkeley, 1st Earl of Falmouth, from whom he was divorced in 1684, and secondly, Lady Morlaud, but had no children from either marriage, so the baronetcy became extinct on his death.