“He was this acerbic, quick-witted, brilliant mind, and yet he would melt in the sight of a child,” the Law & Order: SVU star shared about her late castmate and friend

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Mariska Hargitay is reflecting on the softer side of her late, longtime friend and costar Richard Belzer.

The Law & Order: Special Victims Unit actress opened up on Thursday about how she and the cast are mourning the loss of the 78-year-old actor, who died Sunday.

“What a heart and soul,” Hargitay, 59, told Savannah Guthrie on the Today show. “He was family and taught me so much about taking risks and creativity and trust, and he brought so much joy to the set.”

She continued, “And boy, did this man love children. He was this acerbic, quick-witted, brilliant mind, and yet he would melt in the sight of a child.”

She summed up, “He was just such a beautiful and complex [person], and it was such a privilege to know him.”

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Hargitay’s comments come after she first spoke of Belzer’s death in a touching tribute on her Instagram, which she captioned with a simple broken red heart emoji.

“Goodbye my dear, dear friend. I will miss you, your unique light, and your singular take on this strange world.” Hargitay, 59, wrote on Instagram. “I feel blessed to have known you and adored you and worked with you, side by side, for so many years.”

“How lucky the angels are to have you. I love you so very much, now and forever,” the post concluded.

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Before adding his own statement, fellow costar Christopher Meloni tweeted a photo of Hargitay feeding Belzer on the set of the show.

He followed up with a separate tweet, this time featuring a photo of himself kissing Belzer on the cheek. “Good bye mon ami. I love you,” he wrote, along with the hashtag #TheBelz.

Belzer’s family shared that the actor died peacefully in his sleep at his home in Beaulieu-sur-Mer, France, with wife Harlee McBride and oldest daughter by his side.

The family shared an exclusive statement with PEOPLE Thursday, sharing further details on the star’s sudden death.

“We are overwhelmed with the beautiful and heartfelt memories, admirations and love from Richard’s family, friends, acquaintances and admirers,” Belzer’s loved ones wrote.

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“It has been truly helpful for us, his family, in traversing through this challenging time. So thank you,” Belzer’s family added. “We have had a delay in making a statement in regards to his passing because, although he did have several health issues that had been difficult but not terminal, he experienced quite a sudden decline in health that caught us completely off guard, which lead to his passing.”

“His youngest daughter was unable to be there with us, but will be joining us soon. Due to the sudden nature of his passing, we apologize that we were unable to reach [out] until now, as we needed the time to process through this, gather ourselves and our thoughts,” the statement continued.

Belzer’s family concluded, “We so appreciate the outpouring of support from all of our family and friends. And thank you so much for those of you that have been so respectful of our need for privacy and solace during this difficult time.”

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The cause of his death is still unknown. However, a small family service will be held Friday afternoon in Colomars, France.