2:08 PM PT -- Zayn Malik has issued his own personal tribute to late One Direction member Liam Payne ... expressing his sadness in a heartbreaking Instagram upload.

Alongside a photo of himself and Liam seemingly napping during their 1D touring days, Zayn shared his regret for never thanking LP for helping him through "some of the most difficult times," including when he was homesick at 17.

As he continued, Zayn remembered Liam as being "head strong" and "opinionated," admitting they "butted heads" at times. Nonetheless, Zayn said he "secretly respected" Liam for his give "no f**ks" attitude.

Zayn signed off his note by expressing his love for Liam, who he praised as "the most qualified" musician.

Louis Tomlinson is sharing his grief following the death of former One Direction bandmate Liam Payne ... posting a poignant tribute to his social media.

In the wake of Liam's death in Argentina Wednesday, Louis posted to Instagram, where he shared he is "beyond devastated" by his peer's untimely passing.

He wrote ... "Yesterday I lost a brother. Liam was somebody I looked up to everyday, such a positive, funny, and kind soul."

Louis recalled the early days of their friendship, when they were first partnered -- along with Harry Styles, Niall Horan, and Zayn Malik -- to form One Direction on UK's "The X Factor."

He noted ... "I was instantly amazed by his voice but more importantly as time went on I got a chance to see the kind brother I’d longed all my life for."

Louis went on to praise Liam's songwriting ability, hinting he and his late friend had discussed collaborating again in the near future.

He added ... "And for the record, Liam was in my opinion the most vital part of One Direction. His experience from a young age, his perfect pitch, his stage presence, his gift for writing. The list goes on. Thank you for shaping us Liam."