The highly rated Manchester United and England under 20's goalkeeper, joined the Mariners on a deadline day loan until January 2017.
The 19 year old joined the Old Trafford club as a 14 year old from Carlisle United, where he spent 6 years as a junior. His performances during the 2014/15 season also saw the exciting keeper shortlisted for United's Jimmy Murphy Young Player of the Year.
Dean has been a strong presence in the Manchester United Under 21's and was their number 1 keeper in Nicky Butt's UEFA Youth League side last season. In February 2016, Henderson was recalled from a loan spell at Stockport County to be part of Manchester United's first team squad in their FA Cup tie vs. Shrewsbury Town.
In August 2016, Dean's recent eye-catching performances lead to a call up to Aidy Boothroyd's England under 20 squad to face Brazil in Kidderminster in September.