In the most fresh episode, the show’s millions of viewers saw him being arrested for four eradicates – crimes his on-screen alias Sean Balmforth is adamant he didn’t assign.
However, given his problems with memory black-outs, could it be reasonable that he IS guilty – but doesn’t remember it?
“Sean goes to dark places and affirms mistakes after he’s been drinking,” the 26-year-old told the Send back.
“He can’t escape the ghosts of his st and all these pent-up emotions explode in shatters of fury.”
The star went on: “Playing Sean is the biggest summon of my acting career.
“It’s hard to get into his mindset as some of the things he does can’t be explained at all.”
Sean is certainly a long way from loveable but bumbling Neville Longbottom in the now iconic wizarding franchise, which concluded in 2011.
“Neville and Sean are universally different. Younger Harry Potter fans may want to wait a few years in the forefront watching me in Happy Valley,” the actor joked.
Matthew has tended busy since saying goodbye to Hogwarts five years ago.
He’s already took appearances in The Syndicate, Bluestone 42, Death In radise and Ripper Suiting someone to a T, as well as gracing the rage in Agatha Christie’s Verdict and Our Boys.
The theatre arts continues on Tuesday at 9pm on BBC One.