The Boyzone star and his bandmates - Keith Duffy, Mikey Graham and Shane Lynch - spent the evening before the singer's funeral last month at a Dublin church because they wanted to be together for one last time.
Ronan said: "We didn't want him to be alone in the church and nor did his mother Margaret because he was afraid of the dark.
"We got four sleeping bags and laid with him. It was the most moving experience of my life. It was beautiful. We sat on the pews and we sat on the floor."
The four singers were determined to stay as close to their late bandmate as possible, and even shunned comforts offered by the priest.
Ronan explained to Britain's The Sun newspaper: "At one point the priest came up and said, 'Lads, won't you lie up on the alter? At least it's got carpet down.
"But we wouldn't go up there. It was the only time we'd ever had stage fright."
Ronan - a devout Catholic - admits Stephen's sudden death has caused him to question his religious beliefs.
He said: "I just don't understand t. Where has he gone, why was he taken? I question my faith constantly but I'm a believer so I try to think there must be some sort of logic behind it, that God wanted him."
Stephen died aged 33 from an acute pulmonary oedema, a build-up of fluid in the lungs, at his holiday home in Majorca on October 10.
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