Big sister Sadie and dad Brian celebrate baby Billy's arrival

The former international and Leinster captain looked the picture of joy with his young daughter after news broke that he has another addition to his growing brood.

Dressed in a peak cap and with a look of sheer delight on his face he monkeyed around with his little girl on Friday before the pair went to visit his beautiful wife Amy in Holles Street Hospital - and, of course, the new member of the clan.

O'Driscoll said he was "delighted" at the arrival and the doting father couldn't hide his excitement following the birth on Thursday evening.

His social media fanbase reacted immediately to the news, with many commenting on the pressure on Billy now that he had the same initials as his famous dad - 'BOD'.

One sports commentary website tweeted: "Unconfirmed reports that Rob Kearney is the only man BOD and Amy Huberman trust to hold their new baby".

Meanwhile, a radio station superimposed a baby's face onto an Irish jersey beside the words "B O'Driscoll Jnr" on a future team line-out.

Bookmakers immediately started offering odds on the baby boy following in the sporting footsteps of his legendary father.

The odds of Billy playing rugby for Ireland are 100-to- one, according to Paddy Power bookmakers.

The bookmakers have put young Master O'Driscoll at a hefty 500-to-one to captain the Lions at some stage.

The former rugby star and his actress wife recently celebrated their fourth wedding anniversary, and had been revamping their Dublin home in preparation for their new arrival.

While in the late stages of pregnancy, Amy described their baby news as perfect timing.

"It's lovely timing with Brian finishing.

"It's exciting and I'm really excited for Sadie as well," she said.

"She doesn't understand at all though, not a bit. It'll be a new thing for her to play with - I'm sure she'll understand by November.

"Brian is feeling very excited - so it's all change. Two kids - it sounds so responsible," she added.

Afterwards O'Driscoll was spotted celebrating in none other than Eddie Rockets.

He also took some time out to give a shout-out to a local coffee shop which had offered a free cup of coffee to little Billy.

The rugby great was passing by a sign with the words, "Congratulations, free coffee for Billy O'Driscoll" when he remarked on Twitter: "Son, if I can give you one piece of advice, never look a gift horse in the mouth", along with a picture of the sign.

Brian - who hung up his international and club jerseys in May after a 15-year career - has revealed he knew after just eight weeks that he wanted to marry Amy.

The Dubliner said his initial meeting with the TV star didn't go to plan, but after spending some time with her he knew she was the one.

"After eight weeks I had a fair idea I wanted to marry her, I have no problem with saying that," he said.

The couple's first child was born in February 2013.