What is the deputy prime minister’s role in singapore?

Much has been hyped about GKY and his role as DPM. I can’t find much info on the job scope of a DPM and read from the news in the past that the DPM covers for the PM when he is overseas or on leave etc. GKY and other past DPMs have their own portfolios and ministries to look after so im not sure if they do the actual job of leading and running the govt. Does the DPM have other roles/ powers or is it just a title but without much actual power?