Cameron Bancroft carried his bat for an unbeaten 206 as Gloucestershire were bowled out for 385 by Kent on the second day of their County Championship match at Bristol.
The 24-year-old Australian shared a last-wicket stand of 111 with Matt Taylor, who made a career-best 36, and by the end of the innings had batted for more than eight and a half hours, facing 393 balls and hitting 23 fours and a six.
Bancroft's score was just five short of his best, the 211 he made for Western Australia, against NSW at Perth in 2014-15.
It was the first time he had reached three figures in two spells with Gloucestershire.
The right-hander was named to tour Bangladesh with the Australian Test side in 2015 before that series was cancelled due to security concerns.
He made his international debut in Australia's Twenty20 side against India in January 2016.
By the close of a day's play, which did not start until 1:30pm because of rain, Kent had replied with 2-60, losing opener Sean Dickson for 20 and nightwatchman Adam Milne for a duck.
Gloucestershire had resumed their first innings on 5-242 and soon plunged into trouble as Darren Stevens (3-50) sent back Jack Taylor and Kieran Noema-Barnett.
Milne (3-91) then struck twice in an over, leaving the hosts 9-274 and in grave danger of wasting Bancroft's efforts.
The opener had begun the day on 124 and was still short of the 150-mark when last man Taylor walked to the wicket.
Together they frustrated the Kent attack and ensured Gloucestershire of a meaningful total.
Bancroft moved to his double hundred with a three through the off-side off Mitchell Claydon.
It was Claydon who finally ended Kent's misery as Taylor was caught at short extra cover by Daniel Bell-Drummond.
Bancroft had not given away a chance in a tremendous display of concentration and every fielder moved to shake his hand as he left the field.