Gordon Brown today suggested Jeremy Corbyn was a “phase” in politics.
The ex-Prime Minister said the current Labour leader would not “go on forever”.
He said: “Everything’s a phase.
“I mean Jeremy himself is going to accept that he – nobody goes on forever.
“We’re all phases, we’re all sort of part of it.
“Politicians have a short shelf life actually in terms of life at the top.”
Mr Brown was party chief and PM from 2007 to 2010, having been Chancellor for a decade during Tony Blair's premiership.
Mr Corbyn, 69, seized the Labour leadership in 2015 and won a second landslide victory the following year.
His popularity has been compared to a cult, but he confounded critics with his shock general election performance last year.
Mr Brown told BBC1's The Andrew Marr Show: “Jeremy is a phenomenon and he is reflecting people’s concerns about a whole range of issues, some of which I’m myself raising in the speeches I’m making.
“But, you know, we go through phases in politics.”