"He's one of the biggest rock stars in the world".

Even permanent residents on Planet Bertie surely couldn't stretch to such a definition of the former taoiseach.

So it was clearly Black Sabbath and MTV star Ozzy Osbourne, not Bertie Ahern – who also conducted an in-store book signing at Eason's O'Connell Street yesterday ? that music fan Bernard Walsh was talking about.

You could perhaps understand the confusion, given the hitherto unrecognised similarities between the two.

Both are currently promoting their autobiographies, and appeared on the Late Late Show on Friday night to discuss their lives.

They also share an international profile, have been known in the past to enjoy a drink or two, and got to the very top of their respective fields.

At yesterday's book signings, it was also clear that they share another trait: neither is exactly camera shy.

For Bertie, who began his signing a little earlier than the 3pm starting time advertised in-store, this also involved handshakes and brief chats with anyone who greeted him.

By comparison, at his event earlier yesterday morning, Osbourne was greeted with chants of "Ozzy Ozzy Ozzy" as he coolly descended the store's escalator.

Asked what he thought of the size of the capacity crowd, he turned and gave a one word reply: "Fantastic."

Then the coat came off and it was down to work, signing copies of I am Ozzy priced at €13.99.

By yesterday afternoon, the store had sold around 500.

Complete with talking 'Ozzy doll' tucked into his shirt, Walsh had joined the queue to meet his idol (there was no queue until he and his pal Christian Coleman got there) at around 8pm on Friday night.

They had waited outside until this morning, before getting tickets number one and two of 350 issued to Osbourne fans. "I have all his albums, and around 240 CDs from his Black Sabbath days and onwards," Walsh breathlessly explained, his son, also named Bernard, smiling proudly beside him

By 11.15am, the crowd stretched around the corner as far as Arnott's on Abbey Street. Four hours later, and Eason's was a very different place indeed.

Staff at the shop, fresh from the pandemonium of the Osbourne signing, appeared somewhat more relaxed.

Most striking too was the change in the clothing profile of the "signees". Where the "rocker uniform" of black everything – tee-shirt, jeans, leather jacket – had dominated earlier, those present yesterday wore brighter, less monotone attire.

The man himself was clearly in relaxed, Bertie as "man of the people" mode – rather than the tough party enforcer which he is at times portrayed as in his epic €16.99 tome.

While by no means comparable in size to the crowd which Osbourne had attracted, those present to meet Bertie were no less ardent in their devotion.

"I think he will go down in history for what he did in the North," Sarah Wilson, who had travelled from Tullamore for the day, told the Sunday Tribune.

Her support was echoed by Sr Anna from the Marino Institute in Dublin.

"We all make mistakes, but he has so many other redeeming qualities," she said. "He's a very hard worker and I know that for a fact."

Ozzy fan Bernard Walsh, meanwhile, was nowhere to be seen.