Tony Blair has admitted that if social media was around during his university days he would never have gone on to become prime minister.
On a TV programme, he was shown a picture of him aged about 21 appearing to make a rude gesture which he called "highly embarrassing".
The ex-Labour leader said there would have been "bad stuff" from his days in a band, long before his political career got started.
Mr Blair, 63, sang and played guitar in rock group Ugly Rumours while he was studying at Oxford in the 1970s.
Speaking about the photo, he told host Matt Forde: "Let this be a warning to any young person who wants a political career.
"That is one of the very few pictures of me that is obviously highly embarrassing. Today with social media, just be careful.
"When I was in the band, if we had had social media at that time, I would certainly not have been prime minister."
Asked what people would have seen he laughed and said: "Bad stuff."
During the interview on TV channel Dave, Mr Blair also spoke about his views on Britain's relationship with the US under President Donald Trump.
He said if he was PM now he would feel it is important to "establish a working relationship" with the property tycoon.
He said: "People always want me to criticise Theresa May over this but I think the British prime minister should always get on well with the president of the United States, if it's possible.
"It has got its challenges obviously.
"But it is important because in the end there are many, many things we are going be working on together in different parts of the world."