During his final run at Wembley Stadium for his "Together, Together" tour, Harry reflected on the journey that brought him from boy-band superstardom to selling out one of the world's most iconic venues ... saying "I wouldn't be on this stage if it wasn't for four friends of mine that were a massive part of this journey."

The singer continued to shout out and thank each of his former bandmates -- Niall Horan, Louis Tomlinson, Zayn Malik ... and his "dear friend Liam."

Styles adds ... "These nights, and everything that I learned in this time, the friendship, everything, none of this would be possible. I wouldn't be here without you. Thank you so much."

Liam's parents Geoff and Karen were reportedly even in the crowd to witness Harry's touching tribute to 1D, and particularly their son, in person.

There was no surprise reunion or cryptic tease about the future ... just genuine gratitude from Harry, who made it clear he still credits One Direction and the friendships he built with helping shape the career that landed him on the Wembley stage.

The "As it Was" singer's older sister Gemma Styles also took the stage with a heartwarming speech about her younger brother, to congratulate him on all his recent success.

Styles has now notably surpassed Coldplay's and his ex Taylor Swift's previous records for amount of performances at the famed stadium ... Coldplay with 10 shows and Taylor with 8.

One thing's certain ... a few heartfelt sentences were all it took to send Directioners into full-blown nostalgia mode.