Bellew's predecessor Christoph Mueller joined Malaysia Airlines in May 2015 and stepped down in September past year.
He said: "It is Ireland's greatest company".
Malaysia Airlines officials called cited the "unexpected announcement by Ryanair" and said its board would meet "in due course".
For Ryanair, Bellew's return on December 1 comes as Europe's busiest airline is trying to recruit additional pilots and persuade existing pilots to stay with the offer of new, improved conditions to avoid a repeat of the cancellations. "They need my help and there is a big challenge", he says.
Bellew had been primarily involved restructuring MAS's fleet with the aim toward fulfilling Khazanah plan to relist the airline's shares on the stock exchange in 2019, Reuters reports. "However, a week later, the call came and in life we can really never say never".
Bosses for the budget airline said that they have been swamped with applications for the pilot jobs. "People always ask me how do I cope with government interference. I am looking forward to being close again to my family and friends 14 hours away in Ireland".
Shahril, who was first rumoured to be a front-runner for the post following Christoph Mueller's resignation last April, was group managing director of Prasarana Malaysia Bhd from September 2010 to Jan 1, 2015.
Khazanah had also clarified that it did not interfere with Bellew's authority as MAS board is already tasked to follow through on the MAS Recovery Plan.
Bellew was director of flight operations before he left Ryanair in 2014.
Meanwhile, Liow, when asked about the possibility of the CEO replacement, said it all depended on Khazanah Nasional Bhd as it was the airline's major shareholder.
Transport Minister Datuk Seri Liow Tiong Lai said the ministry had not received any information about Bellew's departure, and was still waiting for the full report from the national carrier.
Mueller, formerly CEO of Ryanair's Irish rival Aer Lingus, later joined Emirates as its chief digital and transformation officer. The Kuala Lumpur-based carrier stated that Bellew has "expressed his commitment to Malaysia Airlines" during a press conference on 27 September. Just another 4%-5% in revenue monthly and it should move to profits. He discloses that the airline's revenue increased by 7% in the second quarter of the current financial year. The product is improving visibly: new widebody planes, new lounges, new loyalty programme, new website and better operations in Kuala Lumpur.
"So much (management) turnover makes the attempted turnaround even more challenging", said CAPA Center for Aviation Chief Analyst Brendan Sobie. Bellew, then the chief operating officer (COO), took over the helm in July past year.