Chelsea defender Tomas Kalas firmly believes Boro will be even stronger this season.
The Czech Under-21 international was given special permission by the Stamford Bridge club to join Boro in Marbella, ahead of completing the formalities of a season long loan deal.
Kalas, who put to paper on Friday morning in Spain, made 17 appearances for the club last term after joining from Chelsea in January on loan, and he says it was an easy decision to return to the club this time around.
"I'd already decided at the end of last season that if Chelsea would like to get me on loan again this would be my first choice, so it was easy when I heard I could stay," he said.
"It's been easy to adapt because I know the lads. I know Marbella because we came here last year so it's been easy.
Tomas Kalas has joined Stewart Downing, Jonathan Woodgate, and Alex Baptiste in signing up for 2015/16. Have you?
"I think we're still building the team. It's a mix of everything. Everyone is still working on it and I think we will be stronger than before."
While last season ended in disappointment for Boro, it also ended in frustration for Kalas, who was reduced to the role of spectator for those final few games after loan ended before the Play-Offs.
"Obviously I wanted to be involved," said Kalas.
"Those were something special at the end because you were playing for promotion and I didn't have a chance to help the team.
"It was a bit disappointing I couldn't play, but this is a new challenge and hopefully we can get promoted without the Play-Offs."
Kalas witnessed the terrific support on offer from Boro fans last season, though, culminating in 38,000 at Wembley, and the player had proved popular during his time on Teesside.
"It's always important because they are the 12th man on the field and when they are behind us in each game, it's a great help for us," he added.