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“Simon was one of the first people Louis called after he’d told his family. Louis was so excited and he wanted to tell Simon himself,” the source tells PEOPLE.
The music mogul, 55, and Tomlinson are good friends and partners in their work.
Cowell is the man behind One Direction, and earlier this year, Tomlinson launched a new record label under Syco, his mentor’s company.
“Simon was absolutely delighted for Louis and told him that becoming a dad was the best thing that had ever happened to him. He told him if he ever needed any advice to let him know,” the source says.
Cowell became a father for the first time on Valentine’s Day 2014 when his girlfriend Lauren Silverman gave birth to their son Eric.
Despite being overjoyed with fatherhood, Cowell has confessed to never changing a diaper!
“Simon knows Louis already has lots of experience with babies and adores kids,” adds the source.
“Louis’ youngest twin brother and sister are only 17 months old and he’s incredibly close to all of his seven siblings — and his mum is a midwife.
“But adjusting to being a dad will be a change, of course, so having Simon’s advice when he needs it means a lot to Louis.”
With Briana – AKM-GSI
Meanwhile, Tomlinson’s friends believe he will find it “relatively easy” adjusting to being a dad — and say he can’t wait to experience daddy duty.
“Simon has even offered to give Louis a ride on his private plane anytime he needs to fly between the U.K. and the U.S. to see their baby,” the friend says.
Cowell regularly commutes by private jet between his international offices in the U.K. and the U.S.
Tomlinson is currently looking for an L.A. home close to Jungwirth so he can spend as much time as possible with his baby.
After Tomlinson shared his exciting news with Cowell, the mogul kept the secret to himself, and despite his excitement for the boy-band star, he didn’t tell his closest friends.
“It was early days and Simon was overjoyed for Louis, but he said it was Louis’ news to tell his colleagues and friends in time,” the source explains.
Cowell has spent the past few weeks in mourning for his beloved mom Julie Cowell, who recently passed away.