So who really was the father? Was Brahma the father of Shiva, or was Shiva the father of Brahma?

Gurudeva! So who really was the father? Was Brahma the father of Shiva, or was Shiva the father of Brahma?” asked a perplexed Shaunaka.
“Haha!” laughed Suta. “Shiva is the father of Brahma. But when Brahma created the whole world, then Shiva entered it as Rudra, His son. That way, the Universal Father got Himself a father.”
( From the book SHIVA, The Ultimate Time Traveller.)