Mercer, 26, joins England’s most-capped men’s player Ben Youngs on the list of names already confirmed to play for the BaaBaas in the showpiece event at Twickenham Stadium on Saturday 22 June (kick-off: 5.15pm).

The Barbarians – led by Kiwi coach Robbie Deans – will face off against the Flying Fijians with the Killik Cup on the line, with tickets on sale now from Ticketmaster, Ticketek or the RFU starting from £55 for Adults and £28 for Under-16s*.

Tickets for the event also include entry to the Qatar Airways Cup showdown between South Africa and Wales, with the two international heavyweights going toe-to-toe at 2.00pm, ahead of Barbarians vs Fiji.

Mercer began his career with Bath Rugby and was nominated for World Rugby Junior Player of the Year in 2017 after captaining England to an U20 Six Nations Grand Slam and the World Rugby U20 Championship final. 

He enjoyed two years filled with success in France following a move to Montpellier Hérault, where he won the Top 14 title and was named the league’s Player of the Year in 2022.

The explosive No.8 returned to England and the Premiership with Gloucester Rugby in the summer of 2023, and despite a two-month spell on the sidelines with an ankle injury, Mercer’s performances for the Cherry & Whites have continued to catch the eye – most recently delivering a man-of-the-match display against Exeter Chiefs to send Gloucester into the Premiership Rugby Cup final.

Mercer is relishing the prospect of another appearance in Barbarians colours this summer, and expects the sparks to fly against Fiji with both sides set on winning while also entertaining a bumper Twickenham crowd.

“I’m absolutely delighted to be involved with the Barbarians again this summer,” he said. “I loved the opportunity to represent the BaaBaas in November 2022 against the All Blacks XV; it was incredibly special to pull on that jersey for the first time and we were on the right end of the result as well.

“Moments and memories like that are the reason you play rugby, so it’s really exciting for me to play again this summer in what should be a brilliant match against Fiji.

“I think it will be two very similar outfits going head-to-head, two teams that want to play fast, exciting rugby.

“The Fijians were one of the best teams to watch at the recent Rugby World Cup, certainly the most-improved team there, and they’re going to want to come to Twickenham and put on a show once again.

“It’s going to be a great battle between the BaaBaas and Fiji on the day, so I’d definitely encourage rugby fans to get down there on June 22 to watch the games. With South Africa vs Wales on ahead of us as well, it should be an unmissable afternoon of rugby.”

This will be Mercer’s second time representing the BaaBaas following the Gloucester No.8’s Player-of-the-Match showing in the 35-31 Killik Cup victory over the All Blacks XV in November 2022, while he has also played against the Club on two occasions – for England in May 2018, and for Gloucester in October 2023.

Mercer added: “Everyone remembers what happens in the Barbarians’ matches, but the week beforehand is just as special as well. It’s all about getting to know each other as a group of players, creating bonds with different individuals who you haven’t played with before.

“I’m really looking forward to getting back to Twickenham again – I’ve played there a few times now, but the stadium still has the same aura for me and every time you get to run out there is a privilege.

“Last time with the BaaBaas was at Tottenham Hotspur Stadium, this time obviously it’s Twickenham, and being involved at venues of that calibre just goes to show what big occasions these matches are.

“BaaBaas matches are great learning opportunities as well. You’re training with some of the best players in the world, and all the coaches are world class. I had the pleasure of working with Scott Robertson and Ronan O’Gara last time – two of the very best in the business – and to work with Robbie Deans on this one is amazing, so I am really excited for that opportunity.”

General admission tickets are on now – visit Ticketmaster, Ticketek or RFU to secure your seat.

Each ticket will cover entry for both South Africa vs Wales (K.O. 2pm) and Barbarians vs Fiji (K.O. 5.15pm) on Saturday 22 June, starting from just £55* for Adults and £28* for Under-16s. For a 10% discount on groups of 10 or more, please visitwww.eticketing.co.uk/rfu/events.

Hospitality packages are also available now, starting from £179 per person – visit www.twickenhamstadium.com to purchase now. 

*booking fees apply