In 1599 he was appointed to the command of 150 foot, and was actively engaged during the rebellion of Hugh O'Neill; and it appears from a letter of his to Lord Shrewsbury that he even endeavoured to procure the assassination or banishment of O'Neill but in this he was unsuccessful.
The collection appeared with a dedication to Gilbert Talbot.
Gilbert and Sullivan | Shrewsbury | James Earl Jones | Prince Edward, Earl of Wessex | Louis Mountbatten, 1st Earl Mountbatten of Burma | 7th United States Congress | Herbert Kitchener, 1st Earl Kitchener | Earl | Frederick Roberts, 1st Earl Roberts | Earl of Derby | Earl Warren | Earl of Pembroke | W. S. Gilbert | Robert Harley, 1st Earl of Oxford and Earl Mortimer | Earl of Warwick | Thomas Wentworth, 1st Earl of Strafford | Edward Smith-Stanley, 14th Earl of Derby | Earl of Shrewsbury | William Pitt, 1st Earl of Chatham | Simon de Montfort, 6th Earl of Leicester | Richard Neville, 16th Earl of Warwick | Humphrey Gilbert | Gilbert | Earl of Leicester | John Scott, 1st Earl of Eldon | Shrewsbury School | Robert Devereux, 2nd Earl of Essex | Robert, 1st Earl of Gloucester | Edward Harley, 2nd Earl of Oxford and Earl Mortimer | Earl of Devon |
She is sometimes confused with another Portuguese lady, Beatrice, wife of Gilbert Talbot, 5th Baron Talbot and subsequently of his steward, Thomas Fettiplace of East Shefford in Berkshire.
He left another son known as Rhys Mechyll(d.1244), who had a son named Rhys Fychan ap Rhys Mechyll and a daughter named Gwenllian Mechyll, who eventually became his heiress and married Gilbert Talbot(d.1274), grandfather of Gilbert Talbot, 1st Baron Talbot(d.1345/6).
In 1596, Segar accompanied the Earl of Shrewsbury to invest Henry IV of France with the Order of the Garter, witnessing Henry's famed Royal entry into Rouen.