Andrew told reporters after attending a service at the Chapel at Royal Lodge Windsor that he feels "very sorry and supportive of his mother," who he said is feeling the death of Philip "probably more than everybody else" and has been "stoic" in her grief.
"She described it as having left a huge void in her life, but we, the family, the ones that are closer, are rallying around to make sure that we are there to support her, and I know there's a huge amount of support not just for her, but for everybody as we go through this enormous change," he said.
Andrew added that the entire royal family is "feeling a great sense of loss" comparing Philip's death to losing "almost the grandfather of the nation."
"He was a remarkable man, I loved him as a father. He was so calm. If you had a problem he would think about it," said Andrew. "He was always someone you could go to."
Philip, the duke of Edinburgh and the longest-serving consort of a reigning British monarch, died on Friday at the age of 99 after undergoing an unspecified heart procedure March 4 for a pre-existing condition and spending several weeks at King Edward VII's Hospital.
He will be laid to rest on Saturday in a ceremony that adheres to some royal traditions, but will comparatively low-key for a royal funeral. The service will be televised.
Per current public health guidelines, no more than 30 people can attend a funeral in Britain.