Byrne moved to Birmingham and into the posh Tamworth neighbourhood after his brother David was shot dead at the Regency Hotel in February 2016 and the Criminal Assets Bureau targeted his wealth.
When Kavanagh was nabbed and placed in custody pending charges for wholesale drug importation, he placed Byrne in charge of his mob.
But sources say Byrne became increasingly reclusive and was terrified that he would suffer the same fate as his brother from rival gangs.
Byrne, like other key members of the Kinahan organisation, has lost everything. His house at Raleigh Square in Crumlin, south Dublin, has been boarded up and is in the possession of the State, his business is gone and he no longer returns to his native Dublin.
He had moved closer to 'Bomber' and his operation in 2017 after becoming increasingly isolated in Ireland and under the attention of the Garda's Drug and Organised Crime Bureau.
Sunday World tracked him down to the West Midlands in 2019 where we photographed him tending to his gardens, pruning his rose bushes and hosting barbeques like his other well-to-do neighbours, who included Premier League footballers, wealthy entrepreneurs and millionaire professionals.
But the Dublin thug has now fled the UK as he fears a backlash from the collapse of 'Bomber's' business and the ongoing trawl of law enforcement for those involved in organised crime.
"His head is gone for a long time," a source said.
"He's lost his nerve and he is afraid of police and rivals.
"Like the rest of them, he is on the run now and feeling cornered."
Byrne, like other Kinahan gang members, hid behind the guise of a businessman who made his money buying and selling second-hand cars, but sources say he has suffered with anxiety over the past few years since 'Bomber' became the target of the UK's National Crime Agency (NCA).
With his brother-in-law, their boss Daniel Kinahan and his cousin, murderer 'Fat' Freddie Thompson, he had led mourners at the lavish mafia-style funeral of his brother David - but just a month later officers from CAB raided his home in Dublin.
Detectives with back-up from specialist units had to use an angle grinder to get into the property during a raid where they discovered a panic room, a Jacuzzi and drinks cabinets stocked with fine champagnes.
His used-car company, LS Active Car Sales, was also raided and €1million in luxury cars seized.
The company, which he ran with co-director Sean McGovern, was later dissolved.
A month later Byrne returned to Ireland for a family party and was arrested by officers who quizzed him about his lavish lifestyle - but later left Ireland for good.
Liam and David Byrne were the scourge of south Dublin for decades and were both involved in the bloody Crumlin-Drimnagh feud.
They later rose up the ranks of the Kinahan cartel and spent years living between Dublin and Spain.
But it was their brother-in-law 'Bomber' who became the real boss as he in turn rose up the ranks of the Kinahan mob, operating its UK and Ireland wing and settling in as No2 to Daniel Kinahan.
Earlier this month Bomber was handed down a 21-year sentence at Ipswich Crown Court for organising drug shipments into the UK through a complex import and export operation that used modified machinery to hide drugs and cash from customs and police.
It was gardai who made the breakthrough into the operation when they raided his weapons HQ in Dublin in January 2017 and seized an arsenal of guns and one document which led them back to cargos travelling in and out of the West Midlands.
Bomber and his cohorts partied and celebrated deliveries unaware that the NCA had launched Operation Hornstay, an undercover operation which would carefully place him at the very top of the chain of command.