The 21-year-old defender initially joined Palace from Bohemian in the summer of 2022, and went on to make 45 appearances for the Eagles’ Under-21 side over the next three seasons in Premier League 2.
As well as wearing the captain’s armband on numerous occasions in 2023/24, Grehan earned a place on the first-team bench when Palace visited Plymouth Argyle in August 2023.
He spent the latter half of 23/24 on loan at Carlisle United, and the second half of 24/25 back at Bohemian, where he played 18 times, scoring three goals.
Grehan now joins a Doncaster side who recently won the EFL League Two title, and who will compete in the third-tier next season.
Everyone at Crystal Palace would like to thank Seán for his efforts at the club, and wish him the very best for the future.