This avenue was named after William J. Twaddell, who was a draper, in North Street in Belfast. He was also a member of the first Northern Parliament. He was assassinated on Monday May 22, 1922 in Lower Garfield Street. Whilst no one has ever been charged with his murder, there are various suggestions who may have been responsible for his killing. In his book, John J. Marshall states he was killed by "three young men who hid in a cul-de-sac at the rear of Mayrs' (now Sinclair's premises) and shot him as he was passing to Royal Avenue from his place of business".
Historian Jason Burke in his popular podcast Historical Belfast devotes an episode to North Street and includes details of the assassination of William Twaddell in 1922. Twaddell had been elected the previous year as the Member for West Belfast of the Northern Ireland Parliament.
https://www.buzzsprout.com/1047775/episodes/15418539-exploring-north-street