The 21-year-old centre-back impressed on trial at the back end of the 2021/22 campaign, before joining Crystal Palace permanently from Bohemian in the summer of 2022.
He made 36 appearances in all competitions in his first season in south London, scoring against Braga in the run to the Premier League International Cup final.
In 2023/24, Grehan started to captain the U21s side and earned a place in the first-team matchday squad against Plymouth Argyle in the Carabao Cup. He made 19 appearances in total for the U21s in 23/24, also earning a new contract in the process.
This season, Grehan has made 18 appearances for the U21s - scoring once and registering two assists. He now returns to Dalymount Park to be a part of Alan Reynolds’ side at the start of their 2025 campaign.
Everyone at the club wishes Seán well on his loan spell.