Winning a Grand Slam is a massive boost going into a World Cup and the Welsh put in their best performance of the Six Nations.
Clinical Wales rose to the occasion with the roof open and rain lashing down in Cardiff on Saturday to end a six-year wait for a Six Nations title and claim a first clean sweep since 2012.
Wales climbed above Ireland to hold second spot in rugby's official world rankings, and they will head to the World Cup in Japan later this year - Gatland's swansong - as major title contenders. Today was a nightmare for Johnny Sexton.
"I am proud of the players it is not about me it is about the players they were playing for themselves their families and Wales", said Gatland.
"We have to be more consistent, dust ourselves off and hope we finish strong in the World Cup".More news: Suspect arrested in murder of reputed mob boss
"We lost to two very good sides and we have to address why".
Wales trained with the roof closed at their traditional eve-of-game captain's run on Friday.
"Knowing that it was my last Six Nations game, you want it to be a fairytale and you want to win and to win in such a place like this would have been massive for the team but would have involved us having a massive performance", said Best.
"I've got to have that belief and self-confidence in us, and if I can portray that on to the players in some small way then hopefully they can believe it as well".
"They scored after a couple of minutes and you're always under a little pressure and we didn't respond overly well to that pressure, giving up penalties".More news: Wolves Have Knocked Manchester United Out Of The FA Cup
This comes after Ireland coach Joe Schmidt accused Wales of breaking tournament protocol by circumventing his side in the discussions whether the roof should be open or closed.
He said: "I'd like to take my hat off to Wales and Gats".
"We've won 23 of our last 26 Test matches, we've finished third in the Six Nations and once upon a time that wasn't the catastrophe that it is today for Ireland", added the head coach.
"We are just trying to slip under the radar we know on our day we are capable of beating good teams", said Gatland.More news: Beto O'Rourke announces run for USA presidency