"The countless messages of love and support we have received this week have truly overwhelmed ourselves and the Gately family.
"We thank you from the bottom of our hearts for each and every one of them."
In a trembling voice, he added that Gately would be given "an unforgettable send-off" in Dublin.
Keating appeared to have a new tattoo on his arm with the dates 76-09 as a tribute to Gately, who was 33 when he died.
Reading from a statement, the singer continued: "Stephen lived to perform and truly loved being centre stage.
"You can be sure he's looking down now wishing we'd move over so he could flash a smile for the cameras one more time."
Keating admitted the future of the band was "too hard to even think about" but whatever happened "nothing will ever be the same without our dearest friend Stephen".
He also appealed for the media to continue respecting their privacy.
No flowers
Thousands of fans and celebrities are expected at the funeral.
Boyzone 'overwhelmed' by support
Friends and neighbours have been cleaning the church and surrounding areas in preparation for the ceremony.
Instead of flowers, mourners have been asked to make donations to the Caudwell Children Charity, for which Gately was an ambassador.
Boyzone yesterday visited Father Declan Blake at the church to discuss funeral arrangements.
The group are expected to stay with Gately's body in the church overnight, and are likely to sing at the ceremony.
Gately's manager Louis Walsh has confirmed he will not appear on The X Factor this weekend as he attends the funeral.
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