The 19-year-old made his competitive debut for the Hammers at Anfield, coming on for the final seven minutes of the encounter which ended in a 3-0 win for Slaven Bilic’s side.
Cullen has revealed that he swapped shirts with Liverpool midfielder James Milner after the match, only to ask the England international to give his jersey back.
“It was a surreal feeling straight after the game, what with us not having won at Anfield for a long, long time, so to go there and win 3-0 and get on the pitch for a few minutes at the end made for one of the best days of my life,” the youngster wrote on West Ham’s official website. “I’m absolutely chuffed.
“I managed to swap shirts with James Milner at the final whistle, but then I had a bit of a panic because I wanted to keep my Premier League debut shirt too!
“Luckily, I was able to get it back so it’ll be great to have two shirts, one for my Premier League debut and also one from a full international like James.”
It is unlikely that Cullen will get to play regularly for the West Ham first team this campaign, but he could be given chances from time to time as the season progresses.
West Ham are back in Premier League action next week when they take on Newcastle United at the Boleyn Ground.