The 73-year-old actor portrays a man stricken with the condition – which affects cognitive function – in ‘The Last Days of Ptolemy Grey’ and he took on the role because his mother, grandfather, aunt and uncle all suffered with the syndrome.

Samuel admitted whenever he fails to remember something, it causes him concern, though he thinks he is “OK”.

Asked if his family history has made him afraid, he said: “Of course. I have times when I can’t remember a name that I know I know. Or walk in a room to get something and go, ‘Why am I in here?’ But I also still remember pages of dialogue a day. So, do I think about it? Yes. Am I worried? I’m 73 … 74? 73 …

“See, like that! But it had happened to my mum and my grandfather by now. So I think I’m OK. For the moment.”

The ‘Snakes on a Plane’ actor remembers the last time his mother, who died in 2012, properly recognised him.

He told Sunday Times Culture magazine: “I remember the last time my mother called my name.

“She was watching TV and a film of mine was coming out. I popped up on the screen and she looked at me and said, ‘Oh, Sam.’ That was it.”

After that, Samuel could see his mom getting angry and frustrated when she looked at him.

He said: “I don’t know if she was running through faces in her mind or seeing me from when I was a little person. Or as this big person.”

The ‘Pulp Fiction’ star admitted his daughter Zoe, 39, has curbed his use of social media out of concern his humour would be taken the wrong way so he is now more cautious about what he says.

He admitted: “People are always calling me about doing a podcast, but I can’t talk for an hour without saying something f*****-up.”