"The post ended with the hashtag, "#TheBrotherhood".
Allen averaged a team-best 3.5 assists during his junior season, but his scoring average was down more than seven points per game from his sophomore year.
While there has been no official announcement, it appears as though Duke's starting point guard will hold off on the National Basketball Association and return for at least one more season.
"I'm a firm believer that when something feels right, you go with it", Allen said.
Airplane crashes in Portugal near supermarket, killing four
The aircraft had only just taken off from Tires airfield when it "exploded" mid-air and plummeted towards the ground 2km away. A spokesman for the local emergency services, Andre Fernandes, said the plane was headed for Marseilles in France.
Allen will try to rebuild his draft stock after a disappointing 2016-17 season.
Even so, his presence on next year's Duke team provides some needed continuity.
He also dealt with disciplinary issues when he was suspended for multiple incidents of tripping opponents on the court.
That nonconference finale in Greensboro, N.C., on December 21 became the third time Allen tripped an opponent that calendar year. "I love being a Duke student - and continuing to be part of the university culture is something I don't take for granted". Other than Allen and possibly Jackson, Duke has four other veteran scholarship players on the roster, none of whom scored a total of 40 points previous year. Guard Frank Jackson could return, although still undecided, and big man Marques Bolden will be back.