The following summer the 29-year-old took an extended sabbatical from the game, including a stint on the BBC's Strictly Come Dancing, before returning with Saracens.
However, after just four games for the Watford-based club, Henson moved to Toulon in the Top 14 where he has featured three times.
His Wales future appeared in doubt after an incident following Toulon's 21-9 win over Toulouse, but he was given a reprieve earlier this week and will now join up with the Welsh squad after Toulon were denied a play-off place with a final day defeat to Montpellier.
Gatland's squad features six new faces including exciting Dragons No. 8 Toby Faletau, while 22-year-old Sam Warburton will captain the side in Cardiff.
Uncapped props Ryan Bevington and Scott Andrews, hooker Lloyd Burns, lock Lou Reed and centre Scott Williams are all included alongside Faletau.
Meanwhile Stephen Jones will have the chance to earn his 100th cap as he battles with Scarlets teammate Rhys Priestland for the fly-half jersey.
Gatland will be without injured regulars Jamie Roberts, Bradley Davies, Gethin Jenkins and Leigh Halfpenny while James Hook is getting married on the same day.
And controversial No. 8 Andy Powell, who was this week released by club Wasps, has also missed out on selection.
"We have selected some exciting youngsters who have been chosen on form in the knowledge that there are a few players who are being rested or are injured for this game, but it means they have a chance to impress," said Gatland.
"It's a great opportunity for us to look at some players that have been hitting their form over the last few weeks.
"These are really exciting times for us as a squad, the Rugby World Cup is on the horizon and we begin our preparations with this first up match against the Barbarians before two intensive training camps in Poland and then our final three matches in August.
"Sam Warburton takes over the captaincy mantle from Matthew Rees, who is rested. Sam is one of the leaders in the squad and will benefit from the experience of captaining the side after having such an impressive Six Nations campaign."
Forwards: Paul James (Ospreys), John Yapp (Blues), Ryan Bevington (Ospreys), Scott Andrews (Blues), Huw Bennett (Ospreys), Richard Hibbard (Ospreys), Lloyd Burns (Dragons), Alun-Wyn Jones (Ospreys), Ryan Jones (Ospreys), Luke Charteris (Dragons), Lou Reed (Scarlets), Dan Lydiate (Dragons), Toby Faletau (Dragons), Josh Turnbull (Scarlets), Sam Warburton (captain) (Blues)
Backs: Tavis Knoyle (Scarlets), Mike Phillips (Ospreys), Rhys Priestland (Scarlets), Stephen Jones (Scarlets), Gavin Henson (Toulon), Scott Williams (Scarlets), Jonathan Davies (Scarlets), Shane Williams (Ospreys), Aled Brew (Dragons), George North (Scarlets), Morgan Stoddart (Scarlets)