Jordan Anderson, 22, was found dead at his father's home after suffering from a mystery illness.
Jordan, from Hull, East Yorks, who appeared to be fit and healthy, is said to have doted on his three-year-old son, who he shared a name with.
His partner of seven years, Lauren Gowan, 20, is due to give birth to their second child - a daughter - at Christmas.
She said: "Jordan was so loving and respectful. He was a brilliant dad to our little boy and he would have been the same to our daughter.
"I can still remember the scan, when we were asked if we wanted to know the sex of the baby. We said we did, and the lady said we have ‘a beautiful little girl’.
“Jordan looked at me and smiled. He was so proud. He couldn't wait to meet her.
"Both of our children are going to grow up knowing all about him."
Jordan’s mother, Linda Anderson, 40, who is also mum to Shannon, 15, and Jayden, eight, paid tribute to her "golden boy".
She said: "Jordan was cheeky and happy. He was my first-born and really looked after my other two. He was really protecting.
"He was looking forward to the arrival of his daughter. Jordan liked to party with his mates, but when he found out they were having a little girl, he told me, 'I have to calm down a bit now. I need to look after her.' What Jordan said, he meant."
Sister Shannon wrote on Facebook: "Losing my one and only big brother is one of the hardest things I'm ever going to go through. He was the one that was there when I needed and always there to have a go at me when I was naughty.
"He always had a massive smile on his face and always knew how to make a bad situation good. It doesn't seem real, I feel like he is gonna walk through the door. Every time I close my eyes I see you there with your cheeky smile and your chip in your tooth."
Jordan’s aunt, Wendy Willis, 51, added: “Jordan idolised his partner and son. Jordan junior is the spit of his dad.
"Just a few days ago, Jordan wrote on Facebook how he couldn't wait to meet his princess daughter."
An inquest into Jordan’s death on October 19 is expected to be heard in March.
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