The former Daily Mirror editor will quiz Elton about his spending sprees and his career.
Morgan will also interview a number of big celebrities including Simon Cowell, 51, about John for the ITV show which will air next month.
The 45-year-old has recently grilled Susan Boyle and Cheryl Cole about their personal lives on the programme.
Boyle, 49, told Piers on Saturday night's show that she panicked and thought 'the dream was over' when she ended up in the Priory.
The Scottish singer said she went there for treatment because she was exhausted.
She said: 'I felt that the dream was over, a bit of a nightmare, but a turning point.
'For two days I was thinking about myself, what my position was, was I stable? I knew I was, I was just tired.'