Long derided as 'Neverkusen' for their failure to win a major title for decades, Leverkusen became the first-ever team in the Bundesliga to complete a full season without a loss following a 2-1 victory over Augsburg in the season finale on Saturday.
The club hailed the achievement by giving themselves a new nickname on their social media channel - 'Bayer 04 Neverlusen'.
"It is an exceptional season, not only in Germany but in Europe," Alonso said in a press conference. "We deserve now to be part of that history of European football. In 20 years we will look back and we will say 'we did that'.
"It is an important day for the club. We have to be proud of the way we played. 90 points and undefeated," he said. "We need a bit more time to value this title. The first Bundesliga title but a big Bundesliga title victory."
Alonso's team also stretched their European record unbeaten run across all competitions this season to 51 matches as they look to add two more titles next week.
Leverkusen face Atalanta on Wednesday in the Europa League final before taking on Kaiserslautern in the German Cup final on May 25.
"I believe it (the unbeaten title win), but I need more time. But we have no time because we have the next big goal (on Wednesday). It is unique opportunity," Alonso said.
"We will remember this day. It is a special day to have the league trophy here and having done it undefeated. This team has now been engraved in Bundesliga history."