After chatting with Molly, who has leukaemia, and her family, Foster heard how much the 12-year-old would like to watch her beloved Watford play Liverpool. So he made her a promise.
He said Molly could be a mascot for the fixture and so, last weekend, when the league leaders visited Vicarage Road, Foster was true to his word.
Molly went behind the scenes at Vicarage Road, met the players and was led out by Foster ahead of kick-off on a truly unforgettable day for her and Watford fans.
"Ben's my best friend," said Molly. "He's so kind."
Foster was not the only goalkeeper at Vicarage Road on Saturday to show kindness.
His Liverpool counterpart Alisson gave Foster his shirt after the match for auction to raise funds for the fight against leukaemia.
So the legend that is @alissonbecker has given me his shirt from the game on Saturday night to raise funds for @cureleukaemia again 👏👏🙌🙌 The highest bidder will get the shirt so anybody seriously interested get in touch on Instagram or in the replies on here👍👍 pic.twitter.com/DTXKPnfu99— Ben Foster (@BenFoster) March 2, 2020