The 6-foot-5 Allen jointly made the announcement with coach Mike Krzyzewski in a school-released statement.
After All-American honors as a sophomore, Allen's scoring dropped more than 7 points per game and he displayed immaturity on the court, earning a one-game suspension for repeatedly tripping opponents.
He was rewarded with Preseason Player of the Year before the 2016-17 season, but failed to live up to the expectations, averaging just 14.5 points, 3.7 rebounds and 3.5 assists per game. Allen would have likely been a first-round pick if he left after his sophomore year but he regressed during his junior year and was surpassed by Luke Kennard as Duke's go-to scorer.
"The last few weeks have provided the opportunity for a lot of reflection and prayer", Allen said in a release.
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With Allen back in Durham, the Blue Devils have solidified themselves as a top 10 team.
Allen studied the options and decided returning to Duke was the best option.
That nonconference finale in Greensboro, N.C., on December 21 became the third time Allen tripped an opponent that calendar year.
Allen's controversy from this season stemmed apparent tripping situations against opposing players. He'll try to revive his stock as a senior next to Duke's latest star-studded freshmen class, led by big man Wendell Carter Jr. and guard Gary Trent Jr.