Tributes are flooding in for Robert Carradine ... and his "Lizzie McGuire" TV wife Hallie Todd is remembering him as family, not just a costar.

Hallie shared a heartbreaking IG photo of them together and revealed their bond went way beyond set life ... saying over 25 years their families became inseparable ... celebrating birthdays, graduations, Halloweens and Thanksgivings side by side.

Hallie called him brave, strong, kind, with a wicked sense of humor -- adding Robert and his family were "probably my most treasured personal gift" from working on "Lizzie McGuire."

She wasn’t alone -- Jamie Lee Curtis also posted an emotional tribute, recalling how they met on set and how she later bonded with Robert’s real-life daughter, Ever, who’s now an actress herself ... she also posted a tribute to her father.

The loss is a heavy one. Robert -- also known for "Revenge of the Nerds" and "The Long Riders" -- died at 71 after taking his own life following a nearly two-decade battle with bipolar disorder.

If you or someone you know is struggling or in crisis, help is available. Call or text 988 or chat 988lifeline.org.