The Dragons star is fresh off winning the Champions League title with Real Madrid and could be forgiven for having his mind elsewhere but Williams believes he will report to the Welsh training camp as exuberant as he always is.
"He is a player who has always been there when we have needed him," said Williams.
"We are going to need him through this tournament definitely, it is on the world stage and everyone will be watching.
"His experience will be valuable in and around the dressing room. He has the most experience of all of us of big occasions, and he normally he doesn't let us down."
Wales meet Sweden in a friendly in Solna on Sunday before setting their sights on their opening Group B clash of the European Championships which takes place against Slovakia in Bordeaux on June 11. England and Russia are the other teams to make up the group.